Monopoly Capital
In 1966, Sweezy published "Monopoly Capital: An Essay on the American Economic and Social Order" with Paul Baran. The book elaborated evidence for and implications of Sweezy's stagnation theory, also called secular stagnation. The main dilemma modern capitalism would face, they argued, would be how to find profitable investment outlets for the economic surpluses created by capital accumulation. Because of the increase in oligopoly this took the form of stagnation as monopolistic firms reduced output rather than prices in response to overcapacity.