The great depression started after WWI, WWII was actually one of the factors that helped end it.

Glad someone said it, FDR did a little bit to help the economy, but it was definitely foreign dependency in the early years of WW2 (before we were in it) on American products such as weapons, oil (yes we actually made a shit ton of oil back then), and steel. Even today our economy is still driven by these three products.