Already in The German Ideology (1845) he specifically made the point that the productivity increases inherent in a capitalist economic system was a prerequisite for a successful socialist revolution as otherwise redistribution would just make want common, and the same class struggles would start all over again as people fight to get out of poverty (like what happened in the Soviet Union, China, where the party organisations became the new upper class).
In the Communist Manifesto he and Engels spelled out how they saw capitalist productivity increases eventually lead to over-production and under-employment, and that this, according to Marx, is what will eventually lead to an intensification of class struggle and finally enable a socialist revolution as economic productivity under capitalism reaches its peak.