Simultaneities of World-System Development:

        Cities , Empires and Climate Change

        Christopher Chase-Dunn
        Department of Sociology
        Johns Hopkins University
        Baltimore, MD. 21218 USA

A research proposal to be submitted to
the National Science Foundation Sociology Program August 15, 1995
        Project Summary

        The world-systems perspective is a structural approach for understanding the
developmental trajectories of national societies and the international political economy
as a whole. It uses a longer temporal perspective and a larger spatial scale than most
other theoretical approaches to social change.
Recently the temporal perspective has been deepened even further by scholars who are
analyzing the continuities and differences between the modern intersocietal system and
earlier systems. This proposal outlines a research project that will compare intersocietal
 networks over very long periods of time in order to answer questions that have emerged from
recent extensions of the world-system perspective to earlier periods. 

The main problem addressed by this proposed research is:

 Do empires and/or cities grow and decline simultaneously in regions that are distant
 from one another and, if so, what are the causes of these simultaneities?

        The study of the relationships between urban growth, empire size and climate is an
 old topic, but the comparative world-systems perspective brings new light to it. The unit
of analysis I will use to examine cities, empires and climate change is the PMN
-- the political/military network -- a set of polities that are interacting with one
another by means of alliances and/or warfare. 

        The focus of this research is the problem of "simultaneities."
Andre Gunder Frank (1994) has postulated, for the Eurasian world system as a whole,
the existence of 200 year phases of  expansion and contraction beginning in the Bronze Age.
 Recent research (Chase-Dunn and Willard 1993; Chase-Dunn and Hall 1994) has found
preliminary support for simultaneities of urban growth and changes in the territorial
 size of empires in Near Eastern and Far Eastern PMNs from the middle of the first
 millennium BC until the sixteenth century AD. These pilot studies indicate some support
for the hypotheses that important connections linked Eurasia in to a single interactive
 system much earlier than most scholars have believed. My research will improve the data
base for examining the simultaneity hypothesis and examine three possible explanations
of this phenomenon. One possibility is that urban growth and the territorial sizes of
 empires were affected in both regions by climate changes and their effects on agricultural
 production. If climate change was the main cause of simultaneous growth and decline in the
distant regions, interactional factors would be disproven. Evidence of climatic change for
each regional PMN needs to be gathered and compared with the sequences of urban and empire
growth and decline to test this hypothesis. Other possible causes of simultaneous
growth-decline sequences are changes in interactional factors such as long-distance
trade patterns or changes in relations with intervening pastoral nomads. Data on trade,
 migrations and warfare with steppe-nomads will be gathered in order to examine these

        The world-systems perspective was developed to interpret and explain the developmental trajectories of modern national states and
 the international political economy as a whole (Wallerstein 1974, 1979; Shannon 1989). The main concepts are "world-system"
defined as a multicultural economic division of labor, and "core/periphery hierarchy," defined as an intersocietal stratification
based on economic and political/military power. Recent research carried out by social scientists in several disciplines (e.g. ethnography,
archaeology, political science, history and sociology) has extended world-systems concepts to earlier, less-than-global intersocietal systems
 ( e.g. Abu-Lughod 1989;  Collins 1992; Algaze 1993) Andre Gunder Frank and Barry Gills (1993) have argued that the contemporary
 global system is similar to, and continuous with, a single world system that was created 5000 years ago  when cities and states first
 emerged in Mesopotamia.  In contrast with those who study local environments and interactions (so-called "splitters"),
Frank and Gills  are proponents of an approach that emphasizes large scale systemness based on very long-distance trade.
They are "lumpers."
        In order to empirically resolve the debates between splitters and lumpers, Chase-Dunn and Hall (1993) have proposed a
comparative approach to world-systems that redefines key concepts (see below) and proposes a typology of world-systems that
vary from small and egalitarian regional networks of sedentary foragers to the contemporary stratified and complex global
 system. It is this comparative conceptual apparatus that will be employed in the research proposed here, but hypotheses
coming from the "continuationist" school (e.g. Frank and Gills) will also be evaluated.

        Chase-Dunn and Hall (1993) define world-systems as
intersocietal networks in which the interactions (trade, warfare, intermarriage, etc.) are important
for the reproduction of the internal structures of the composite units and importantly affect changes
that occur in these local structures.
 They spatially bound world-systems by analyzing local, regional and inter-regional interaction networks
of three kinds:
This multicriteria approach to spatial bounding produces three nested levels of interaction in most world-systems. Generally bulk goods will compose the smallest regional interaction net. Political/military interaction composes a larger net and prestige goods networks are generally the largest (see Figure 1). For example, the BGN of the Roman Empire was smaller than the system of states and empires (PMN) within which Rome allied and fought. And the system of prestige goods exchanges utilizing the "Silk Roads" linked the Romans with distant Indian and Chinese core regions in a larger Eurasian PGN. Figure 1 may be viewed as representing (roughly) the Eurasian-wide PGN during the era in which it contained separate Far Eastern, Indic and Near Eastern PMNs.
        I will update Chandler's city populations using recently published studies, expand the coverage to cities with 10,000 in
population and gather data for 50 year time points for the centuries before 1000 AD. For many time points Chandler presents
 lists of cities ranked in terms of population size but without numerical population estimates. It will  be possible to use new
studies to make  numerical estimates for some of the ranked cities. It is also possible to interpolate some of these numerical
estimates based on the sizes of cities in the same region (e.g. Chase-Dunn and Willard 1993). In some regional PMNs these
 will be important for estimating the city-size distributions. 

         There are two reasons to expand the data set to include all cities that have a population of ten thousand or more.
Wilkinson (1992a) uses a method of measuring urban growth rates based on counting the number of cities in each region.
This is a useful addition to our arsenal of measures of urban growth, but there is a problem basing this measure on
Chandler's data set because the minimum size of the cities included changes over time. Expanding the coverage of
 later time periods to all cities over 10,000 would make this measure more meaningful. It is also desirable to know
about smaller cities when we are looking for intervening cities between PMNs. And recall also that the time points
 included by Chandler are too far apart for the earlier millennia. These will be filled in to every 50 years to match the
empire size data.

                This job of data enhancement and expansion will utilize substantially the same methods that
Chandler employs (Chandler 1987: 2-13). He uses several methods for estimating the population sizes of
cities --  census figures,  traveler's estimates, size of the built up area, hearth counts, the size of the military, etc.
Chandler will serve as a consultant on this project and I will visit with him for a week in Berkeley to obtain
 information and discuss measurement problems. I will do a search for all the literature that was not available
to Chandler for his 1984 compilation. I will also consult with him about interpolation methods. My project will
code data about the location of cities (longitude and latitude) so that our data will easily fit in to a larger world
history Geographical Information System (GIS).  

Empire Sizes    

        The second data set I will work with is the territorial sizes of empires assembled by Rein Taagepera (1978a;1978b;1979;1986).
Taagepera used maps from atlases to estimate the territorial sizes of empires over the past four millennia. His estimates are for
every 50 years, but his data set has unfortunate holes because he was only concerned with the very largest empires on Earth.
Thus he excludes important regional empires that are needed when we are using PMNs as the unit of analysis and for the purposes
 of constructing size distributions of empires to measure power concentration/dispersion. 
        Taagepera's data on the territorial sizes of empires will be updated by using more recent sources than those that were
available when he compiled his data set. And coverage will be extended to empires that Taagepera excluded because they
were not among the largest on Earth at a particular time point.  We also will be able to add data for Mesoamerican and
Peruvian empires to fill out our PMN cases there. In addition, I will add data on the timing of the events that  led to empire
 expansion and contraction. Usually these were significant wars of conquest. The dating of such events will be useful for
considering the relationship between empire size change and changes in climate.

        Taagepera will serve as a consultant to the project. I will visit him at the University of California-Irvine to discuss
his methods of estimating the territorial sizes of empires and to examine the files from which he produced his data set.
He will also provide suggestions about maps and atlases to be used in extending the coverage of the empire size data set.


        In order to examine climatic variation as a cause of simultaneities it will be necessary to obtain regional data on
climate change for those regions that are found to have high simultaneity correlations with other regions. The  main case
 we will focus on in this regard is the Near East and the Far East. But I will also gather climate change data for all the eleven
 PMNs on which I will have city population and empire size data. 

        Comparable climate change data for the Near East and China over the relevant time periods and for a representative
sample of locations within each region may be difficult to locate. Important local variations in climate change are
well-known, so it  is inferentially dangerous to rely on climatological proxy data from only a few sites. The relevant
aspects of climate change are the amount of average yearly rain fall, catastrophic flood events, and the average temperature.
These affect agricultural productivity and may have indirect effects on urban growth and empire size. One important method
for historical estimations of these variables involves the study of tree rings (dendro-chronology). Some tree ring chronologies
 are being built up for China (Sheu 1994; Graumlich n.d.) but their are  as yet no dendrochronological sequences for
  Mesopotamia. Studies of pollen deposition patterns in lake sediments are used to infer climate change.  Mesopotamian
climate change is being inferred from Persian Gulf sediments and from stratified soils (Nutzel 1976; Weiss 1993).
 Glacial ice cores are also used to infer changes in precipitation. While the urbanized regions we are studying are
generally not close enough to glaciers to make this kind of  evidence useful, we also want to know about weather
changes in intervening peripheral (or semiperipheral) areas. Paleoclimatologists have also used weather diaries
(verbal descriptions of weather events) to reconstruct climate sequences and to verify other proxy indicators of
climate change (e.g. Zhang and Crowley 1989; Wang and Wang 1994). Documentary evidence about the frequency
and location of devastating floods or droughts may indeed be helpful, but it will be desirable to locate less subjective
indicators (such as the Nile height measurements mentioned in Footnote #9 above) whenever possible. I will consult
with experts on climate change at the World Data Center for Paleoclimatology  in Boulder, Colorado and at the
Laboratory for Tree Ring Research at the University of Arizona.


        Warfare is a human  interaction variable that is known to affect both urban growth and the territorial size of empires.
 The  hypothesis about  processes of steppe empire formation and the migration of pastoral nomads out of Central Asia
being the key to simultaneous rise and fall of agrarian empires at both ends of the Eurasian land mass could be supported
 if we find simultaneous increases and decreases in warfare between steppe nomads and agrarian states in both the Near East
and the Far East.  Thomas Barfield's (1989) Perilous Frontier provides the information for the Far Eastern region.
For the Near East  I will use data on warfare obtained by the LORANOW project (Cioffi-Revilla 1991;1994). 


        Ideally we would like to have comparable and reliable data on cross-Eurasian trade by both the Silk Road
and maritime routes over the whole period that we are studying. In practice trade data are quite piecemeal. Nevertheless
 I will probably be able to obtain enough data to make rough estimates of changes over time in the amount of trade
flowing over the different routes linking China, India and the Near East.  Price data are also useful.
Frank  and Gills (1995) have recently argued the importance of the balance of payments in influencing the growth
and decline of states and  regions and as an indicator of core vs. peripheral status.  As demonstrated by Braudel (1979),
  simultaneous and corresponding changes in prices over time in different  localities  are themselves an important
indicator of systemness.  Yearly price data from China and the Near East  will enable us to examine  the simultaneity
hypothesis on a finer time scale than the city population and empire size data. This will also be helpful in evaluating
 the relationship between economic activities and climate change.


        The basic data on empire and city sizes will be used to produce  five different measures. With the city data
we will construct three measures of different aspects of change in city systems. The first measure will be the estimated
 population size of the largest city.  The second measure will examine the shape of the city size distribution
-- the relative sizes of the five largest cities. For this we will use the Standardized Primacy Index (SPI) developed
 by Pamela Walters (1985).  City systems vary with regard to the steepness or flatness of the city size hierarchy.
A very flat city size distribution is one in which the largest cities are all about the same size. A steep city size
distribution corresponds to what is referred to in the settlement system literature as "urban primacy."
This means that the largest city is much larger than the other cities in the system. The SPI compares the actual
distribution of city population sizes with a hypothetical rank-size hierarchy in which the largest city is twice
 the size of the second largest, the third largest is one third the size of the largest, and so forth. Deviations toward
flatness from the rank-size norm are  assigned negative scores, while deviations toward steepness are assigned positive
values that increase with the steepness of the city size distribution.  A third measure of urban systems is the
number of cities within a region that are larger than a certain cut-off size. This can be understood as a measure
of city density. We will improve upon David Wilkinson's(1992a) measure based on the number of cities by adding
all cities larger than 10,000 to the data set.  Wilkinson's measure was based on the cities listed in Chandler's compendium.
Chandler's lists drop smaller cities as the number of  larger cities increase. The problem here is that  a change in the
 number of cities may reflect changes in the lower cutoff rather than a real change of the number of cities within
a region. Having a constant cutoff of 10,000 eliminates this problem.
        Two measures will be computed using the territorial sizes of empires. The simplest is the size of the largest empire.
We will also compute a size distribution of empires using our territorial size data on the three largest polities.
We will use the SPI to compute this measure. This will provide an indicator of the relative degree of centralization
 of power in regional state systems.  In order to analyze the direction of causality vis a vis  changes in empire size and
climate I will also  construct a measure of empire size change that codes the month (or year) of key events such as
 wars of conquest that resulted  in changes in empire size.  This will require going back to Taagepera's original files
to determine the timing of events that  led to changes in  empire sizes.


        The main method of data analysis will involve time series correlations and regressions within and across PMNs.
 It will likely be necessary to detrend these variables in order to examine whether or not short term rises and falls are
 correlated. The geometric rises of everything in the nineteenth century will overcome all other relationships. Another
way of getting around this problem is to exclude the years after 1800 AD. 

        In order to evaluate the simultaneity hypotheses we need to correlate rises and falls in the same variables for
different PMNs. This is done by combining the PMNs in the same data set and calculating the temporal correlations (e.g. Figure 3).
We may also want to examine hypotheses about time lags in relationships or loosen the criterion of "simultaneity"
 somewhat by widening the time periods. It will not be possible to calculate meaningful moving averages because
we have 50 year intervals and it will not be feasible to find data for smaller intervals of time, except  for the climate measures.

        Recall that  we also want to examine the question of the direction of possible causal interaction between climate
 change and urban and/or empire growth and decline. In principle the issue of the direction of causality can be determined
 from time series data using the procedure of Granger tests of antecedence.  But Granger causality analysis  is usually applied
to yearly data (e.g. Rasler  and Thompson 1994: 93).  Our fifty-year time points are  too crude for the determination of antecedence.
 If we find significant correlations between climate measures and  urban or empire growth/decline phases we will need
to look at a finer time scale in order to employ Granger tests of antecedence. This can be done for the empire size variable
 by using the  dates of events such as  wars of conquest in which empires expanded or contracted.

        This project will improve existing data sets on empires and cities that are important for our understanding of
world history. These data sets will be constructed so as to fit easily in to a  larger world history  GIS (geographical information system).
This study will produce improved explanations and evidence regarding the causes of urban and empire growth and decline,
 and the interactive relations between distant regions. It will examine the hypothesis of climatological effects on social change.
And it will have important implications for some of the main conceptual and theoretical problems at the roots of the
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