Project summary:

This proposed research examines the causal effects of eight world-system cycles and trends on the occurrence of violent conflict among core states. A world-system model of the causes of wars among the great powers is constructed and tested by operationalizing eight independent variables and four alternative measures of the dependent variable ( core warfare). This model is evaluated regarding its past performance over the last five centuries in order to estimate its usefulness for predicting future world wars. The uniqueness of the research proposed here is that it focuses on trend variables thought to be especially relevant for predicting warfare in the next several decades. The methods of analysis employed are cross-correlation and time series regression. These will produce estimates of the relative sizes of effects and provide better parameter estimates for simulation studies of the future probability of world wars.
 
 
 

An unfunded proposal submitted to the National Science Foundation (Sociology Program).
 

Project Description:

Conflict Among Core States: World-System Cycles and Trends

The world-systems perspective posits the existence of a set of institutional structures, cyclical processes and secular trends that are features of the modern world-system as a whole. These processes have operated within the Europe-centered and now-global system for centuries. A recent reformulation of this schema is presented in Chase-Dunn (1994). The world-system model of cycles and trends is arguably relevant for understanding the causality of both past and future wars among core states. The world-systems perspective combines the logic of geopolitics with the dynamics of competitive capitalism to explain patterns of warfare. The model of cycles and trends has been evaluated empirically by previous research, though much work needs to be done to resolve controversies that previous empirical studies have raised. The research proposed here is designed to resolve these problems and to examine the effects of trends that are hypothesized to be relevant for predicting the probability of future wars among core states.

The scenario of the next several decades that is predicted by a simple extrapolation of world-system cycles is as follows:

The United States hegemony will continue to decline much as the British hegemony did at the end of the nineteenth century. The Kondratieff B-phase (world-wide economic stagnation) that began in the late 1960s will end sometime in the 1990s, perhaps it already has. A new period of relatively greater global economic growth will last from 20 to 30 years. During this period the major core powers [the United States, Japan, Germany (or German-led Europe)] will compete with one another for comparative advantage in the new lead industries of this K-wave upswing: infomatics and biotechnology. This competition and growing scarcities of raw materials and "problems of order" in both the periphery and parts of the core, will cause the current disequilibrium in the distribution of military power (the virtual U.S. monopoly) to move toward a more balanced distribution of military power among core states. This is another way of saying that Germany and Japan will build up their military capabilities. The multipolar world of economic power will equilibrate into a multipolar world of military power.

Late in the K-wave upswing (i.e. in the 2020s), the world-system schema predicts a window of vulnerability to another round of world war. This is when world wars have occurred in the past. Intensified rivalry and competition for raw materials and markets will coincide with a multipolar distribution of military power among core states. The world-system model does not predict who the next hegemon will be. Rather it designates that there will be structural forces in motion that will favor the construction of a new hierarchy. Historical particularities and the unique features of the era will shape the outcome and select the winners and losers. If it were possible for the current system to survive the holocaust of another war among core states, the outcome of the war would be the main arbiter of hegemonic succession. While the hegemonic sequence has been a messy method of selecting global "leadership" in the past, the settlement of hegemonic rivalry by force in the future will be a disaster that our species may not survive. It is my concern about this possible disaster that motivates this effort to understand how the hegemonic sequence has occurred in the past and the factors affecting hegemonic rivalry in the next decades.

What are the cyclical processes and secular trends that may affect the probability of future world wars? The world-system model is presented in Figure 1.

Figure 1: Factors influencing the probability of future core wars
 
 

This model depicts the variables that I contend will be the main influences on the probability of war among core states. The four variables that raise the probability of core war are the Kondratieff cycle, hegemonic decline, population pressure (and resource scarcity) and global inequality. The four variables that reduce the probability of core war are the destructiveness of weaponry, international economic interdependency, international political integration and disarmament. The probability of war may be high without a war occurring, of course. Joshua Goldstein's (1988) study of war severity (battle deaths per year) in wars among the "great powers" demonstrated the existence of a fifty-year cycle of core wars. Goldstein's study shows how this "war wave" tracks rather closely with the Kondratieff long economic cycle over the past 500 years of world-system history. It is the future of this war cycle that I am trying to predict.

Factors that Increase the Likelihood of War Among Core States

The proposed model divides variables into those that are alleged to increase the probability of war among core states and those that decrease that probability. There are four of each.

Kondratieff waves

The first variable that has a positive effect on the probability of war among core powers is the Kondratieff wave -- a forty to sixty year cycle of economic growth and stagnation. Goldstein (1988) provides evidence that the most destructive core wars tend to occur late in a Kondratieff A-phase (upswing). Earlier research by Thompson and Zuk (1982) also supports the conclusion that core wars are more likely to begin near the end of an upswing. Boswell and Sweat's (1991) analysis also supports the Goldstein thesis. But several other world-system theorists have argued that core wars occur primarily during K-wave B-phases. This disagreement over timing is related to a disagreement over causation.

According to Goldstein states are war machines that always have a desire to utilize military force, but wars are costly and so statesmen tend to refrain from going to war when state revenues are low. On the other hand, statesmen are more likely to engage in warfare when state revenues are high (because the states can then afford the high costs of war). Boswell and Sweat call this the "resource theory of war."

Those who predict that core wars will be more frequent and destructive during a K-wave downturn (Frank, 1982; Bergesen 1985; and Goldfrank 1987) generally assume that economic competition among firms and states is greater during a downturn, and so states are driven to employ military means in their competition with one another in such periods. Goldstein argues that economic competition is also very great during periods of economic expansion.

Hegemonic sequence

All hierarchical world-systems -- chiefdoms, early states, tributary empires and the modern interstate system -- exhibit a cycle of political centralization followed by a phase of decentralization (Chase-Dunn and Grimes 1995). The rise and fall of hegemonic core powers -- the hegemonic sequence -- is the form that this cycle has taken in the modern world-system. This sequence replaced the oscillation between interstate system and "universal empire" that was typical of earlier tributary world-systems. In the hegemonic sequence the multistate structure of the core is maintained. There is never a universal empire, but the distribution of economic and military power oscillates from one in which there is a more or less equal distribution among a set of core states to one in which a single core state has a significantly greater concentration of economic and political/military power.

The two most recent hegemons have been Britain in the nineteenth century and the United States in the twentieth century. The rise and maintenance of hegemony is a function of comparative advantage in leading economic sectors, political/military advantage in the control of international trade, and victory in world wars among core states (Modelski and Thompson 1995). Hegemonic stability theory (e.g.Gilpin 1981 ) supports the proposition that warfare among core states is less frequent and less severe when there is a strong hegemon that acts as power balancer and guarantees the stability of the structure of world power. When there is no hegemon -- when power is multipolar in the core -- warfare among core states is much more likely because there is no powerful hegemon to keep the peace. Thus Figure 1 shows hegemonic decline having a positive effect on the future probability of war among core powers.

Population pressure and resource scarcity

Population pressure is the outcome of population growth in a context of circumscription and ecological degradation. Population pressure is a function of the relationship between population density (the number of people per land area), the resources in that territory, and the technology employed to utilize those resources. As population grows, resources become more scarce because of greater utilization and degradation of the environment, and so it takes greater expenditures of labor and other valuables to produce additional food and other goods.

Resource scarcity and the intensification of competition among core states for raw materials in the periphery have been argued as the cause of world wars in the past. The "lateral pressure" model of Choucri and North (1975) explains World War I primarily on this basis. The relevance of the population pressure/circumscription model to the contemporary global situation is this. The industrial revolution and accompanying advances in public health technologies have lowered infant mortality and increased life expectancy in both the core and the periphery. The explosive growth of population in the periphery and semiperiphery slowed a little during the latest K-wave B-phase, but it is likely to recover in the coming A-phase.

The scale of ecological degradation has expanded from a local and regional phenomenon to a global scale as industrial society has employed ever larger amounts of non-animal energy. Intensification of agriculture and more productive technologies have enabled production to stay approximately even with population growth, though there have been some recent large-scale famines in the periphery. The pressure to continue the expansion of agricultural production is likely to run into resource shortages and global ecological limits in the next several decades. As resources become scarcer, rising competition and conflict over access to these resources will raise the probability of war among core powers. Possible oil shortages are the obvious example.

Inequality

The growing gap between the core and the periphery is a long term trend that shows little sign of abating despite the recent successes of some semiperipheral countries. And within countries in both the core and the periphery inequalities have increased significantly during the K-wave B-phase. Thus overall inequality -- both intranational and international -- has increased in the past decades and many social scientists expect this trend to continue in future decades.

In the semiperiphery there are two groups of countries that need to be considered with regard to the problem of relative inequality. The rapid industrialization of much of the semiperiphery since 1960 has not altered the relative distribution of GNP per capita among the nations of the world, though it has changed the relative distribution of energy consumption (see Chase-Dunn 1989:266). Some of these countries do, however, seem to be moving up in the core/periphery hierarchy, especially Korea, Taiwan, and China. Others are simply running hard to stay in the same place, e.g. Brazil, Mexico and India. In the first group inequalities have not decreased and they may, in some cases, be increasing. This is quite likely to be the case in China. Among the semiperipheral countries that are not moving up inequalities have increased in the last few decades (e.g. Freiden 1982; Wood and Magno de Carvalho, 1988).

If the global gap between the rich and the poor continues to expand in the next several decades this will probably increase tensions between the core and the periphery and also within and among core states. It is entirely possible that the United States will continue along the path toward greater internal inequality that began in the Reagan years. If this happens we would expect increases in racial and class conflict within the U.S. Such a situation would be likely to destabilize the alliances among core states. If either a very reactionary or a very Leftist regime were to be elected in the U.S. during a time of international instability an outbreak of warfare among core powers might result (e.g. Wagar 1992).

Factors that Decrease the Likelihood of War Among Core States

There are four main factors designated in Figure 1 that decrease the likelihood of war among core states. It is these factors that are most often cited by those who contend that future core wars are unlikely.

Destructiveness of weaponry

The most common argument regarding the low probability of future war among core powers cites the existence of weapons of mass destruction that makes full-scale war among states armed with these weapons "irrational." It is contended that everyone can recognize that a war in which such weapons are used is unwinnable because even the winning side would experience massive destruction. The peaceful (in terms of core wars) period since World War II is explained by the bipolar balance of terror that existed between the Soviet Union and the United States.

While I agree that the destructiveness of weaponry decreases the probability of warfare among core states (as indicated in Figure 1), there has been a very long term trend in the increase of the destructiveness of weaponry, and at many earlier points it was claimed that warfare had become so costly that no sane people would engage in it. World War I was not supposed to happen because of the carnage that industrial warfare would cause. During the Cold War it was recognized that a first-strike capability might be developed by one side that would eliminate or greatly diminish the ability of the attacked side to do much damage in return. The balance of terror can easily be unbalanced by the development of new offensive or defensive technologies.

International economic integration

Economic globalization is also offered to explain why future core wars are unlikely. As with military destructiveness, international economic integration is a long term world-system upward trend. For centuries the world-system has been becoming more economically integrated. International trade and investment have expanded, firms have increasingly produce for international as well as national markets. Recently firms have engaged in international joint ventures, international sourcing for production, and global marketing strategies. It is alleged that this globalization of the world economy has proceeded to such a level that nation-states are irrelevant to economic decision-making because economic forces are beyond their control, and capitalists now form a single, unified global class that will no longer use national states as instruments of violent struggle.

The world-systems perspective has long argued that, though the internationalization of capital has been an upward trend for centuries, capital has always been international in the modern world-system in the sense that important firms have contended internationally for shares of the world market. The Great Chartered Companies of the seventeenth century were true precursors of transnational corporations. And the states that competed with one another in the seventeenth century were also subject to the forces of the international economy as well as international military and naval competition. But in the seventeenth century only a few core and semiperipheral states were under the control of capitalists who were trying to extract surplus by means of commodity production and sale, while in the 20th century nearly all states have joined in the game of "international competitiveness." Hence the secular trend.

International economic integration generally decreases the probability of war among core powers because it makes these states dependent on one another and therefore raises the costs of conflict. But there are some kinds of interdependence that may increase the likelihood of conflict among core powers. The long-term trend in trade multilateralization has periodically been reversed during periods of economic contraction and warfare when states became more concerned about the extent to which they were dependent on other states. Also there has been an oscillation in the structure of core/periphery trade relations. During some periods core countries have traded more freely with lots of different countries in the periphery, while in other periods core powers trade more exclusively with a specific set of peripheral countries that constitute their "own backyard." This core/periphery block-formation tends to occur at the same time that the distribution of power among core states is becoming more equal -- that is during the decline of a hegemon (Krasner 1976). In earlier world-system eras this block-formation took the form of colonial empires in which each core state linked tightly with its own colonies. The British Commonwealth was a functional equivalent of block-formation that extended beyond the "end of empire." NAFTA and APEC are potential contemporary functional equivalents of the block-formation process. This kind of regional "international economic integration" is more a consequence of rivalry among core states than a harbinger of global economic integration.

Choucri and North's (1975) study of the causes of World War I points to a phenomenon that they call "lateral pressure" in which core powers come into conflict because they had overlapping spheres of interest in peripheral regions. Overlapping trade networks constitute a type of interdependence, but in this case the outcome was to raise the probability of conflict rather than lowering it. Tieting Su (1995) contends that the current pattern of world trade networks corresponds to a situation of lateral pressure operating in the overlapping interests of the United States and Japan in Pacific Asia and the Middle East (see also Frankel and Kahler 1993).

International political integration

Many observers have noted an upward trend in international political integration since the early nineteenth century. The Concert of Europe was succeeded by the League of Nations, and the League was succeeded by the United Nations. Craig Murphy's International Organization and Industrial Change (1994) tells the fascinating story of the growth of global governance by an international civil society composed of international organizations and led primarily by the liberal internationalists among the global bourgeoisie. Murphy contends that the ideologies and organizations of international liberalism have been important actors in the world-system since the early nineteenth century. If international political integration has been an upward trend for two hundred years it is likely that it has reached a level that decreases the likelihood of warfare among core states.

Though the United Nations is still not a very strong and effective provider of collective security, it has made great strides since the end of the Cold War also ended the stalemate in the Security Council. The growth of international organizations has been geometric since World War II, and many observers speak of the formation of a truly global polity, an international community, an international civil society, and the integration of separate groups of national capitalists into a single global capitalist class. The formation of the Trilateral Commission and the Group of Seven represent part of this trend toward international political integration. And international non-governmental organizations have also expanded phenomenally.

If the trend toward international political integration continues in the future it should lower the probability of war among core states. The creation of international regimes in which member states come to accept common norms of procedure for resolving disputes ought to lower the probability of disputes developing into interstate war. And the strengthening of the ability of the United Nations to mediate conflicts and to intervene to halt violence should also reduce the probability of warfare. Robert Keohane (1984) argues that the growth of international normative regimes has ended the cycle of hegemonic rivalry. The "world polity" school in sociology has also emphasized the importance of world-wide normative agreements that have emerged in the nineteenth and twentieth centuries (Meyer 1987). Boli and Thomas (1993) contend that the patterns of expansion and differentiation that they observe in international non-governmental organizations between 1875 and 1973 are important indicators of the construction of a world polity that transcends national-level organization.

A related type of international political integration is analyzed by Bruce Russett (1993). Russett shows that regimes that are electoral democracies are unlikely to engage in interstate warfare with other similarly democratic regimes. Electoral democracies are about as warlike as other kinds of regimes, but the wars in which they engage are with un-democratic regimes. Since 1815 there have been no interstate wars among democratic regimes as defined by Russett. Twelve possible exceptions (out of seventy-one interstate wars) are shown to not fit Russett's criteria for democracy or for interstate warfare. The empirical fact of no, or few, wars between democracies is credibly established by Russett.

Russett notes that the proportion of all states that have electoral democratic regimes has risen greatly since the nineteenth century and so he predicts a future trend toward this form of government that can lead to a permanently peaceful international system of states that share democratic values. While I agree that electoral democracies are less likely to engage in warfare with other electoral democracies, and that the trend toward the expanding proportion of regimes that are democratic in Russett's sense is likely to reduce the probability of war among core powers, I am less optimistic about the idea of a permanent "democratic peace" emerging in the next several decades.

It is well-known that even very stable and long-term democracies tend to become less democratic during periods of international tension. And, in countries where democratic institutions are less well embedded in the civic culture, international conflict often produces a re-emergence of authoritarian regimes. Thus, even though there has been a trend toward more electoral democracy, we can expect future reversals of that trend during periods of international strain. It is even possible that the trend that Russett points to could increase the probability of war among core states if one core state were to revert to an authoritarian regime in a context in which all other core states were long-term democracies. Such a development might be perceived as such a grave threat to the "democratic peace" that warfare would seem to be justified.

Disarmament

Disarmament undoubtedly lowers the probability of accidental war. There have been great strides away from the brink of the balance of terror since the demise of the Soviet Union. The international effort to limit nuclear proliferation has some chance of succeeding despite the increasing easiness with which nuclear bombs can be produced. But disarmament does not by itself change the institutional basis of interstate warfare. Even if all weapons were to be destroyed, but the right of sovereign states to make war on one another was preserved, a dangerous situation would still exist. This is because the terrible knowledge of how to produce weapons of mass destruction will not perish even though existing weapons are wrecked. And so a situation of conflict among states will likely lead to the reconstruction of weapons of mass destruction. It is sobering to recall that Germany did not begin rearmament after World War I until 1935.

Testing the Model

The proposed project is a continuation and refinement of earlier research on the world-system causes of wars among core states. It is also a new departure in the sense that the focus on the future raises new questions about the past. Several of the trend variables in the model described above have not been analyzed in previous research. These will be studied in order to determine the role that they may have played in past world wars and to help us understand how (and to what degree) they may affect the probability of future wars.

Of course it is impossible to test a model of the future directly. Yet, it is the future we care about the most. The solution is to test models of the past while including variables that we have good reason to believe will be relevant for future events and to use the results to provide better guesses about what will happen in the future. Simulation models of future world-system dynamics (e.g. Kowalewski and Hoover 1994) need a better grounding in studies of the past . The estimates of the sizes of causal effects of variables derived from studies of the past can be used to estimate parameters for simulation studies. The unique focus of my proposed research is to test the effects of trend variables --- those that have been increasing (or decreasing) over the last centuries and are thought to have an increasing effect on warfare. The study of these trends can be used to estimate their future values. These estimates can be used in improved simulations to better understand the future probabilities of violent conflict among core powers. I do not propose to construct a simulation model in this research project, but rather to provide better estimates of the past effects of variables and a better basis for predicting future levels and effects.

The big problem in doing research on the world-system is that processes work slowly and the main system-level "events" are few and temporally far between. This means that we must compare recent decades with centuries past. While the data for recent decades is often good, comparable measures decay as we move back in time. Put another way, the further we go back in time the cruder our measures become. Nevertheless we must go far back in time to get enough variation for causal analysis. For example, if we consider "world wars" to be those wars in which several of the great powers are engaged in warfare with one another, a research design that encompasses only the last two centuries would arguably include only two such wars -- the Napoleonic Wars and World Wars I-II. It is for this reason that we must extend our temporal scope of comparison back to the fifthteenth century, as several other researchers have done (e.g. Boswell and Sweat 1991; Rasler and Thompson 1994; Modelski and Thompson 1995).

Previous Research

Earlier research on the systemic causes of world wars provides a helpful basis for the research proposed here. Some of the main hypotheses in our model have already been evaluated, though not conclusively. One goal of this research is to determine the relative importance of different causal factors proposed by different theoretical approaches. I will also operationalize variables in different ways to determine how differences in measurement (and conceptualization) affect conclusions about causation.

Joshua Goldstein (1988) focused on the relationship between the Kondratieff wave (K-waves -- a forty to sixty year economic cycle) and core warfare. He operationalized warfare as "severity" -- the number of battle deaths per year caused by wars among the great powers (Levy 1983). Analyzing this variable from 1495 to 1975, he found a fifty year cycle of core warfare that corresponds quite closely to his measure of the K-wave. He operationalized the K-wave primarily in terms of price series.

Boswell, Sweat and Brueggemann (1989) used an "intensity" measure of core warfare -- the number of battle deaths as a proportion of the population of Europe at the beginning of the war (also found in Levy 1983). They operationalized hegemony based on the dates for four phases of hegemony (hegemonic ascent, hegemonic victory, hegemonic maturity and hegemonic decline) hypothesized by Hopkins and Wallerstein (1979). K-waves were operationalized three different ways, but were based primarily on prices (1989:16-17;Appendix). Boswell and Sweat (1991) operationalized hegemony in four different ways. Three were based on dummy-coded dates implied by different theoretical approaches. One was a quantitative measure -- Modelski and Thompson's (1988) measure of relative sea power.

Modelski and Thompson (1988) operationalized what they call the "power cycle" (my hegemonic sequence) as the concentration or dispersion of relative naval power among the great powers. Modelski and Thompson (1995) operationalize the economic comparative advantage of rising and falling system leaders (hegemons) by examining the concentration/dispersion in certain lead industries or economic activities. Modelski and Thompson propose a "twin peaks " model in which each power cycle (hegemony) is composed of two innovation-based K-waves that are separated by a global war.

Rasler and Thompson (1994) use naval power and lead industry concentration to examine the causes of global warfare. They operationalize great power war by means of a list of five wars they consider to have been crucial for global-level politics (1994:17;Appendix B) and as military expenditures as a proportion of Gross Domestic Product. Their model of the causes of global war (1994:13) focuses on the dynamics of two interacting processes -- competition among states for control of the global system and competition among states for territory within a regional (European) system. They contend that rise and fall processes at the global level interact with regional (continental) competition to produce global war. In this approach war occurs when a declining global leader perceives a challenge from a rising regional power. Rasler and Thompson operationalize regional power by means of the concentration/dispersion of army sizes among the great powers.

Measurement

I will use the best measures from earlier studies and improve upon them where that is possible. I will also use multiple indicators of each variable and compare the results. As mentioned above I will also include variables that have not been previously examined, but which are hypothesized to be relevant for the future.

The dependent variable: core warfare

There are several problems involved in measuring core warfare. The conceptualization and bounding of the core states is one. Another is the definition and delineation of those historical events that we wish to categorize as core wars. We want to include major wars that involve core states on different sides. And the size or importance of a war should be proportional to the size of the system. This is an important consideration because the system grew greatly over the last five centuries. The most thorough single consideration of all these issues is contained in Rasler and Thompson's (1994) Appendix B. But their conclusions are partly constrained by their emphasis on the distinction between global and regional levels of international conflict and by the "twin peaks" model. These factors lead them to choose five particular wars that they consider to have been important in deciding issues of control at the global level. A less constrained method includes all the wars above a certain size (in terms of number of combatants) in which core states were involved on both sides . These wars are then weighted by quantitative estimates of their magnitudes. I will use five quantitative measures: "severity" (battle deaths per year); "intensity" (battle deaths per year as a ratio to the total population of the great powers); total military expenditures of the great powers; and military expenditures as a proportion of the total gross domestic product (GDP) of the core. I will also use military expenditures as a proportion of government revenues because national accounts information (the basis of GDP estimates) are not available before 1790.

The measures based on battle deaths are available from Levy (1983) for the years from 1495 to 1975. I will improve Levy's intensity measure by weighting it by the total populations of the core countries rather than the total population of Europe.

Long economic cycles

I will use price series as one measure of the K-wave. The big advantage of prices is that data are available over the whole 500-year period of the study. On the other hand many analyst of the K-wave have contended that prices are relatively epiphenomenal, and that economic phases should be measured in terms of production or volumes of trade. I will also construct an economic cycle series based on the international trade of core countries for the whole period from 1500 to the present. A third measure will be composed of national accounts data based on the work of Peter Grimes (1996). This will cover the period from 1790 to the present. Grimes (1993) has found that GDP per capita data do not reveal forty to sixty year Kondratieff waves, but something much closer to twenty year Kuznets cycles. I will investigate the relationship between these production-based Kuznets cycles and warfare among core states.

Hegemonic sequence

I will employ six quantitative measures of changes in the distribution of power among core states to measure the hegemonic sequence. These will include naval power from Modelski and Thompson (1988) and army sizes from Rasler and Thompson (1994). The army size data will include the armies of all core states and major powers (including Russia).

I will also use Modelski and Thompson's (1995) measures of leading sector shares as an economic indicator. In addition I will use the distribution of GDP per capita, trade as a percentage of total core trade, and a composite measure of world-system position operationalized by Grimes (1996). For the years before 1790 I will use data on state revenues. Before the nineteenth century we do not have national account statistics to use for estimating the value of production, but we can produce a rough estimate of the national incomes of the core countries by using Braudel's (1984:312) rule that national income is roughly twenty times the level of state revenues.

Population pressure and resource availability

Population pressure is a difficult variable to operationalize because it depends on the relationship between population density and the resources available to that population. Population density is rather easy to operationalize. It is the total population divided by the land area. In our case we can include the total population of the core states and the total land area of those states. But how can we measure available resources? One way is to use a measure of overall production. This results in a measure of population pressure that has average core population density in the numerator and total GDP of the core states in the denominator. Both of these components are available for the nineteenth and twentieth centuries. For earlier centuries we will use the total international trade of the core states as a proxy for GDP.

Inequality

The discussion of inequality above refers to both intranational and international inequalities. Measures of intranational inequalities are not available for most countries before the last three decades. Thus I will need to rely on measures of international inequality. This will require data on both core and peripheral countries. Peripheral data is much more scarce than data on core countries, and this is a problem for studying early core/periphery inequalities. In the past it has been assumed that real wages in the core were subsistence wages before about 1880 (e.g. Amin 1975) and therefore core/periphery inequalities were small before then. It would be useful to test this assumption more closely. Here we can use data on national production (Gross Domestic Product per capita) from the nineteenth and twentieth centuries. For earlier centuries we can use data on trade per capita, though there are potential problems with this because of the problem of the composition of trade and trade partner concentration.

Destructiveness of weaponry

There is no system-level quantitative measure of the destructiveness of weaponry . Studies such as that by McNeill (1982) make it clear that the "efficiency" of killing is a secular upward trend. But what could we use to approximate the shape of that trend over the relevant time period? Perhaps a measure of the number of people that can be killed by a single combatant per minute would do the job. So swordsmen and archers can kill one or two. Original cannoneers can kill five or ten. Bombardiers with conventional bombs can kill 50 or 100. Bombardiers with nuclear bombs can kill five or ten million. A button-pusher with a multi-warhead intercontinental ballistic missile can kill all the people in the biggest city on Earth -- as many as twenty million, and one button might launch more than one missile, each one wiping out a city. These are approximations to be sure and it is somewhat artificial to imagine that a single combatant does any of these things. But it does correspond at least roughly to the notion of the increasing destructiveness of weaponry. Now we assign dates to the time points at which each of these technologies became generally adopted by the core countries and draw a curve between the midpoints of the ranges specified. Is this "measurement"? No, but it may be the best that can be done for this variable.

International economic interdependence

We can safely restrict the scope of this measure to the core states. This makes measurement more feasible further back in time. As mentioned in the discussion above, international economic interdependence is a multidimensional concept. Thus it is desirable to have different measures. One long-run measure is the total amount of international trade carried on by the core countries. The only problem with this measure is that the populations of the core countries have also risen, so part of the increase in foreign trade is due population growth. The best way to take this in to account is make a ratio of foreign trade to the total population of the core countries. Another measure that is calculable from trade statistics is average (across the core countries) trade partner concentration -- the percentage of all exports (or imports) that come from the largest export (import) partner. When this measure goes down it means that trade is becoming more multilateral.

International political integration

This is a variable that is somewhat difficult to measure over the whole period of this study. I will use the number of treaties of all kinds among states as a rough indicator of international political integration that can be coded back to 1500. For the nineteenth and twentieth centuries much better indicators will be employed. From 1860 I will use Craig Murphy's (1994: 285-92) list of the founding dates (and terminating dates) of international organizations. Each organization will be weighted by the number of civil activities coded by Murphy. The number of activities corresponds fairly well with the budget size (or number of employees )of these organizations and thus provides an estimate of the importance of each organization. The unweighted list indicates an upward trend since 1850, but these organizations are not equally important so they need to be weighted. Because my conception of international political integration is not narrowly "political" I will also employ data on the military activities of international organizations (Bloomfield and Leiss 1969; Coplin and Rochester 1972). Both civil and military activities need to be taken into account in an overall measure of international political integration. I will also include a measure of the number of states in the system that have democratic regimes according to Russett's (1993) definition.

Disarmament

Disarmament presupposes armament -- the stock of available military personnel and technology. This can be indicated by the total number of peacetime military personnel of the core states and military expenditures. Disarmament correspond to peacetime periods in which these indicators are relatively low. We know that military buildups occur in the periods just prior to world wars. Measurement of the relative size of peacetime armaments can tell us whether or not prior low levels of armament reduce the probability of wars, and we will be able to compare levels of armament over the long run. This variable needs to be weighted by a measure of the population and/or the economic size of the core states to make it comparable over time.

Research Design and Methods

The variables I will operationalized are understood to be characteristics of the whole world-system, but some of them use information only for core states while others (e.g. population pressure and inequality) require information on both core and peripheral countries. For most of the variables we have more than one indicator and these have different extents of spatial and temporal coverage. Generally the measures with greater coverage are cruder, but I will collect these for the whole time period (up to present) in order to compare cruder with finer measures. I may be desirable in some cases to "splice" different measures together using information on covariation in order to produce indicators that cover the whole time period.

The temporal shape of measured variables will be determined graphically. The general shape of economic cycles and the hegemonic sequence are already known, though my measurement refinements may produce some new insights. But for the rest of the variables, though it has been assumed that they are upward secular trends, this has not been established empirically. I may find that some of these are also cyclical or are wavy trends.

To examine relationships among variables I will employ cross-correlational analysis and time series analysis using both simultaneous and lagged relationships. Time series analyses will employ a time trend variable to reduce the possibility of spurious effects of unmeasured linear trending, and an additional control will be included -- the dependent variable lagged one year in order to make the main dependent variable a change variable (see Boswell and Sweat 1991:138).

These methods will make it possible to infer the direction and sizes of causal effects of the included independent variables on the occurrence of warfare among core states. The inclusion of the new "trend" variables will enable me to check the conclusions of earlier researchers about the effects of economic cycles and the hegemonic sequence when the trends are controlled. The sizes of the "trend" effects can also be compared with the sizes of the economic cycle and hegemonic sequence variables, and this will have implications for our predictions about future war causation. If these are indeed secular upward trends it will be possible to see how changes in their levels at different periods affect warfare and to use these observations to provide better parameter estimates for simulation studies of the probability of core wars in the future.
 
 

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