That said, I don't find Wallerstein's work to be particularly convincing. A good deal of his theoretical position is predicated upon Braudel's Annales school historical work and Andre Gunder Frank's dependency theory (a kind of warmed over Leninism applied to Latin America). As it turns out, dependency theory is more or less wrong on the facts — it was a plausible sounding theory, but didn't have much of an empirical basis.

Wallerstein's work is an expansion of Braudel's work on the Mediterranean-as-an-economic/geographical-system and on A.G. Frank's dependency theory. Wallerstein posits that the entire global economy grew out of the European/Mediterranean system, and that there's a dependent relationship between the core states (First World industrialized countries) and periphery states (Third World raw materials suppliers). This is basically an updating of Lenin's essay "Capitalism: The Highest Stage of Imperialism", buttressed with a great deal of historical narrative.

If you read Wallerstein's short introduction to WST, World-Systems Analysis: An Introduction, you'll get an idea of what a theoretical spaghetti his thought is when pressed to put it down simply and briefly on the page. And the last third of the book is devoted to a kind of 1960s-counter-culture burnt-out-hippie wishful-thinking about the potential of anti-globalization movements.

If you're really interested in Marxist International Political Economy, I would skip Wallerstein and try Giovanni Arrighi and David Harvey instead. For the more historical stuff, Braudel, Abu-Lughod, and Frank are awesome.