To some degree just "connecting the dots" and forming an understanding of the interconnections of various injustices that i was already aware of. Instead of treating them as isolated treating them as connected and in (dialectical) relationship with one another, and with the whole (capitalism-imperialism).
Learning about the history of my ancestors (they were Bundists and Marxists but don't tell that to the Zionists!) and finally actually listening to some Marxist theory instead of getting it from second-hand sources.
Also i can't emphasize enough how much the Black Liberation Movement radicalized me as a kid. Even though i'm not African the fact that African people need to fight for their very survival under capitalist society against the (u.s.) state and capital, as well as various theories that Black radicals have articulated to organize this resistance were very influential. Really struck home the relevancy of all of these seemingly abstract theories in the present-day struggle.