In this article, we analyse the history of the 1929 crisis, and its political-economic outcome, with emphasis on employment fluctuations in Roosevelt’s New Deal in the USA and the country’s entry into World War II; the Spanish revolution, the French popular front and the civil war and the rise of Nazi-fascism as a product of the defeat of social revolutions. The absence of support on the part of the USSR and the social democracy for the revolutionary projects of the 30s of the 20th century contributed to this defeat; it resulted from the militant support of the German industrial and financial sector for this Nazi project, and of the inaction, if not active complicity, of social democracy and its alliances with semi-Bonapartist powers before Hitler’s rise to power. Its outcome was the greatest tragedy in human history.