There has been recent circulation of the older view that it is World War II, as a kind of giant public works project, which ended the Great Depression. This claim is not consistent with our best knowledge of the subject. To survey the cutting edge of the literature briefly:
Christina Romer writes:
This paper examines the role of aggregate demand stimulus in ending the
Great Depression. A simple calculation indicates that nearly all of the
observed recovery of the U.S. economy prior to 1942 was due to monetary
expansion. Huge gold inflows in the mid- and late-1930s swelled the
U.S. money stock and appear to have stimulated the economy by lowering
real interest rates and encouraging investment spending and purchases
of durable goods. The finding that monetary developments were crucial
to the recovery implies that self-correction played little role in the
growth of real output between 1933 and 1942.
We examine whether local economies that were the centers of federal
spending on military mobilization experienced more rapid growth in
consumer economic activity than other areas. We have combined
information from a wide variety of sources into a data set that allows
us to estimate a reduced-form relationship between retail sales per
capita growth (1939-1948, 1939-1954, 1939-1958) and federal war
spending per capita from 1940 through 1945. The results show that the
World War II spending had virtually no effect on the growth rates in
consumption that we examined.
Further debunking of the WWII idea can be found in this paper by Robert Higgs, who stresses the difference between standard gdp measures and actual economic welfare.
I also find the experience of the Latin American economies convincing. The economic recovery of Argentina, for instance, clearly was due to monetary policy, not fiscal policy, which remained tight throughout the period of recovery. Mexico recovered from the Great Depression relatively quickly and this history also does not fit the fiscal policy view. Later on, most of the Latin economies experienced commodity booms because of wartime demands and again this was not fiscal policy and of course they were not fighting the war themselves. The two countries where fiscal policy played a significant role in recovery are, not surprisingly, Germany and Japan and here I am referring to their prewar spending.