A lot of super-left/socialist/marxist identifying folks don’t like to talk about anything other than class. It throws some wrenches into their logic, and a lot of the old school Marxists were/are pretty damn racist.
Kropotkin was a neat early Marxist writer who did a good job bridging the class/race divide. Showed that most people are tribal and collectivist in small groups, but power and resource access get tied to powerful elites who distort the system. Capitalism is an evolved form of a basic power disparity.
My understanding of the split is that the Kropotkin style thinkers promote decentralization and democracy, while the Leninists went the way of trying to make socialism work from the top down, as in the USSR and China.