Amy Gilligan explains how the contradictions at the heart of capitalism that mean that it is an inherently unstable system, prone to crises.
Suggestions for further reading:
Marx on the law of the tendancy of the rate of profit to fall in Capital Vol 3
Stuart Easterling on Marx’s theory of economic crisis in the International Socialist Review:
Chris Harman, Zombie Capitalism (published by Bookmarks)
Also check out Michael Di Benedetto’s video on Profit: A Numbers Game, But Shit Don’t Add Up Somehow