For a glance at the existential/spirtual/political inspiration for the
World-Systems perspective i would recommend Frantz Fanon's The Wretched
of the Earth. Wallerstein's motivation for WST and many current
adherents comes from an understanding of the human atrocities committed
by the many guises of imperialistic global capitalism. Fanon's work is
a passionate peice which highlights the injustice created by the world
system(while not naming it such). Daniel Chirot has gone so far as to
say (in Skocpol's, Vision and Method in Historical Sociology) that
Wallerstein's is the theory justifying "third world" liberation.
P.S.
Wallerstein was crucial in getting Fanon's work published in English.
Cheers,
Christian Harlow
University of California, Santa Cruz