The greatest contribution that Marx made was the Theory of Historical Materialism. With that theory arrived at as he says by himself and Engels independently, they grasped how historical change is conditioned by the material conditions in society that Man confronts in attempting to survive and produce. The limits of the productive forces that Man finds in society condition the way he is able to produce. The very limited nature of those productive forces for Primitive Man shaped the way he met his needs via Collective, Co-operative action. In turn that conditioned the type of societies he lived in, which were themselves collective and co-operative.
The ascent of Man towards Civilisation is similarly conditioned by the way in which these productive forces are themselves developed as a consequence of the way Man himself reacts back on Nature in developing those productive forces. The ability of man to move to ever higher forms of society ultimately leading to Communism is then a reflection of this continual improvement and development of the productive forces. In the Communist Manifesto, Marx and Engels spelled out the implications of this theory for the way they understood contemporary society - Capitalist Society - and its implications for the class struggle. They spelled out how this scientific view set them aside from other types of Socialists such as the Moral Socialists like Sismondi, who criticised Capitalism for all of its cruelty and vicissitudes, but failed to see that without it, without its development of the productive forces then all of the benefits that Capitalism brings with its development of those productive forces was impossible. Not only was the development of the productive forces impossible without Capitalism, but Capitalism was impossible without all of the cruelty that went with it, because without the expropriation of the peasants a large working-class needed by the factories could not have been made available. Without the kind of exploitation of those workers by the early forms of Capitalism, via Absolute Surplus Value, the accumulation of Capital would not have been possible. But, without a working-class, Socialilism itself is impossible. That is why they concluded that what Capitalism produces most is its own gravedigger!
I had been planning to write a blog in the near future covering some of these issues in relation to the question "Progressive Imperialism?" However, in what started out as a discussion about intervention in Libya over at the Commune, two comrades led the discussion off on to a debate about these issues. To be honest, I am so shocked that anyone considering themselves a Marxist could challenge its basic assumptions, and scientific base that I wondered whether these contributors were really trolls. Whatever, some of the issues involved are important areas for discussion.
As this was a divergence from the actual thread I agreed with comrades at the Commune that I would create a discussion on these matters here. That is the purpose of this post. Anyone interested should, of course, read the series of comments over at the Commune first.