Ow did KARL MARX explain change in human society?

Very demanding profesour with lots of free time so please do your best, and try not to use only acredited academic sources.

many thanks

chris
1. Karl Marx and Frederick Engels 1982. The Comunist Manifesto in Marx and Engels, Collected Workd, vol 38 ( Lawrence and Wishart)
2. Karl Marx 1977 Preface, A contribution to the Critique of Political Economy ( Progress Publishers) handout
3. T Bottomore& M Rubel eds.1956 Marx Selected Writings in Sociology and Philosophy (Watts)