ory being the general one. Classical economists had believed in Say's law, which, simply put, states that "supply creates its own demand", and that in a free market workers would always be willing to lower their wages to a level where employers could profitably offer them jobs. An innovation from Keynes was the concept of price stickiness – the recognition that in reality workers often refuse to lower their wage demands even in cases where a classical economist might argue it is rational for them to do so. Due in part to price stickiness, it was established that the interaction of "aggregate demand" and "aggregate supply" may lead to stable unemployment equilibria – and in those cases, it is the state, not the market, that economies must depend on for their salvation.
The General Theory argues that demand, not supply, is the key variable governing the overall level of economic activity. Aggregate demand, which equals total un-hoarded income in a society, is defined by the sum of consumption and investment. In a state of unemployment and unused production capacity, one can only enhance employment and total income by first increasing expenditures for either consumption or investment. Without government intervention to increase expenditure, an economy can remain trapped in a low employment equilibrium – the demonstration of this possibility has been described as the revolutionary formal achievement of the work. The book advocated activist economic policy by government to stimulate demand in times of high unemployment, for example by spending on public works. "Let us be up and doing, using our idle resources to increase our wealth," he wrote in 1928. "With men and plants unemployed, it is ridiculous to say that we cannot afford these new developments. It is precisely with these plants and these men that we shall afford them."
The General Theory is often viewed as the foundation of modern macroeconomics. Few senior American economists agreed with Keynes through most of the 1930s. Yet his ideas were soon to achieve widespread acceptance, with eminent American professors such as Alvin Hansen agreeing with the General Theory before the outbreak of World War II. 
Keynes himself had only limited participation in the theoretical debates that followed the publication of the General Theory as he suffered a heart attack in 1937, requiring him to take long periods of rest. Among others, Hyman Minsky and Post-Keynesian economists have argued that as result, Keynes's ideas were diluted by those keen to compromise with classical economists or to render his concepts with mathematical models like the IS–LM model (which, they argue, distort Keynes's ideas). Keynes began to recover in 1939, but for the rest of his life his professional energies were largely directed towards the practical side of economics – the problems of ensuring optimum allocation of resources for the war efforts, post-war negotiations with America, and the new international financial order that was presented at the Bretton Woods Conference.
In the General Theory and later, Keynes responded to the socialists and left-wing liberals who argued, especially during the Great Depression of the 1930s, that capitalism caused war. He argued that if capitalism were managed domestically and internationally (with coordinated international Keynesian policies, an international monetary system that didn't pit the interests of countries against each other, and a high degree of freedom of trade), then this system of managed capitalism could promote peace rather than conflict between countries. His plans during World War II for post-war international economic institutions and policies (which contributed to the creation at Bretton Woods of the International Monetary Fund and the World Bank, and later to the creation of the General Agreement on Tariffs and Trade and eventually the World Trade Organization) were aimed to give effect to this vision.
Although Keynes has been widely criticised – especially by members of the Chicago school of economics – for advocating irresponsible government spe