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.

Here is another interesting paper on the topic; it focuses on productivity issues and mean reversion. Here is from a paper by Cullen and Fishback:

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.