"It was only by the crisis of 1929-1930 which shook the capitalist economy of the whole world to its very foundations and the long depression following it that bourgeois economists were forced to interest themselves in problems of this kind. Then, John Maynard Keynes produced his famous theory of employment which dealt with mass unemployment and economic stagnation as tendencies inherent in the modern capitalist system which the state ought to counteract by an appropriate policy of intervention. Partly under the influence of Keynes, partly independently of him, and in some cases even earlier, economic theories betraying similarities to the Marxist theory of reproduction and accumulation began to appear."