All systems change, Capitalism doesn't "pervert" dialectics any more than feudalism did. It isn't perversion so much as it is the progression of dialectics, this is why Marxists describe the dialectical movement as endless spirals. All systems resist the next stage in development, in fact Capitalism is quite a young system in comparison to how long feudalism lasted.

As for Imperialism, I recommend you read Imperialism, the Highest Stage of Capitalism. In it, Lenin describes how Capitalism has grown and morphed since the time of Marx, who didn't live long enough to see Imperialism really become the dominant contradiction upon which all other contradictions rest in the modern world.