Social Subjectivism and Marxism

[ReasonAlone]

I am reading Ominous Parallels, and I have run into a bit of confusion. I will state what I know, and what I am confused over.

I understand that social subjectivism under Kant declares that group consciousness creates reality.

I understand that Marxism grew out of this idea.

I do not understand the connection.

One passage in particular confuses me:

"Later philosophers accepted Kant's fundamental appraoch, but carried it a step further. If, many claimed, the mind's structure is a brute given, which cannot be explained-as Kant had said-then there is no reason why all men should have the same mental structure. There is no reason why mankind should not be splintered into competing groups, each defined by its own distinctive form of consciousness, each vying with the others to control reality."

Mr.Peikoff says that this is the evolution from social subjectivism to Marxism. The "competing groups" are classes in Marxism, of course.Either I am missing the connection, or Mr.Peikoff has forgotten a transition. Help on this would be much appreciated!