The substantive basis of world systems theory is 1500-1800, the age of absolutism and merchantilism, when the "struggle between nations," a world systems staple, was driving history, more or less. The reason being, that nation states were born in struggle, the Dutch against Spain, being the first important one. Also, you've probably noted, that the production of capital play little role in his theory, only its distribution, another sign of merchantilist thinking.
A possible antedote maybe Peter Gowan's, The Global Gamble (Verso), which I'm reading. Best wishes, Jim O'Connor