Are there any particular texts from Engels that you disagree with? I would be interested to know where you think the split is. From my reading, Engels was mostly involved in the philosophical and scientific side of the development of dialectical materialism and it's application into Marxism. Eg. "Dialectics of Nature", "The German ideology", "Feuerbach and the end of German classical philosophy","anti-duhring" etc. I'm not sure where the apparent "brutality" is coming from here?