In the United States, Mattick carried through a more systematic theoretical study, above all of Karl Marx. In addition, the publication of Henryk Grossman's principal work, (1929), played a fundamental role for Mattick, as Grossman brought Marx's theory of accumulation, which had been completely forgotten, back to the centre of debate in the workers' movement. To Mattick, Marx's "critique of political economy" became not a purely theoretical matter but rather directly connected to his own revolutionary practice. From this time, Mattick focused on Marx's theory of capitalist development and its inner logic of contradictions inevitably growing to crisis as the foundation of all political thoughts within the workers' movement.
