“War has several causes. Dictators and others such, to whom war offers, in expectation at least, a pleasurable excitement, find it easy to work on the natural bellicosity of their peoples. But, over and above this, facilitating their task of fanning the popular flame, are the economic causes of war, namely the pressure of population and the competitive struggle for markets. It is the second factor, which probably played a predominant part in the nineteenth century, and might again, that is germane to this discussion.”
John Maynard Keynes, “The General Theory of Employment, Interest and Money”, 1936:381-382
Skidelsky even makes a strong case that it took the War for people to start listening to Keynes:
“In his biography of Keynes, Sir Roy Harrod reports a widely acclaimed speech delivered by his subject to the House of Lords in 1946, the year of his death. ‘But Keynes had been talking in this style ... for some twenty-seven years. Why had his words not been listened to .... ?’ (...) Unemployment as a problem in economic theory may have been sufficient to produce a revolution in the discipline; unemployment was not a sufficient problem to society to produce a revolution in political ideas. If it was not the prolonged experience of mass unemployment that finally broke the hold of nineteenth-century ideas, what was it ? A strong case can be made out for war. ‘Normal’ life could coexist with unemployment; it could not with modern war.”
Robert Skidelsky, “The reception of the Keynesian revolution”, in Milo Keynes, “Essays on John Maynard Keynes”, CUP 1975:89 & 102-103
Kennedy (1999) makes clear that ‘Keynesian’ elements like maintaining aggregate demand were prominent elements in even Herbert Hoover’s policies. Similarly, deliberate inflation was considered by Roosevelt e.g. to help farmers reduce their debt burden. Nevertheless, Kennedy has to write: “In the ninth year of the Great Depression and the sixth year of Roosevelt’s New Deal [i.e. 1938 /TC], with more than ten million workers still unemployed, America had still not found a formula for economic recovery.” (p362) There was contact between Roosevelt and Keynes, but with little effect - Roosevelt apparently regarded Keynes pejoratively as an academic theorist. Then:
“Deprived of adequate public or private means of revival, the economy sputtered on, not reaching the output levels of 1937 until the fateful year of 1941, when the threat of war, not enlightened New Deal policies, compelled government expenditures at levels previously unimaginable.” (p360)
The policy stagnation around 1938 is the more surprising, since Kennedy reports Roosevelt saying on a Fireside Chat at that time (April 14 1938): “History proves that dictatorships do not grow out of strong and successful governments, but out of weak and helpless ones.” (p362)