How is war a cure for economic challenges?

Given the threat of Hitler and the Axis power alliance, President Roosevelt's articulation of the "arsenal of democracy" makes sense. There is little to indicate that negotiations would have worked with the Nazis and that the Axis alliance would have relinquished the claims made on all of the mainland Europe. In this regard, war and conflict were almost inevitable, given the real and valid threat that Hitler and the Axis alliance posed. Any question about this can be resolved in the study of the Holocaust. By itself, this justifies galvanized action as "the arsenal of democracy."
However, it also becomes clear that World War II effectively killed the New Deal. Roosevelt's New Deal legislation was his attempt to pull America out of the Great Depression. While it did have some effect, it was mostly psychological in terms of how Americans viewed the economic crisis. Expansion of government aside, the end result that President Roosevelt sought out of the New Deal came with the militarization of the United States and the progression towards war. A significant drop in unemployment as well as a significant rise in economic growth gave the President what he so yearned for in the New Deal. War became the machine through which economy could function. One of the realities of Roosevelt's "Arsenal of Democracy" was that the Great Depression ended with the advent of war. It becomes a very unsettling reality that the machinery of war is what could solve a nation's economic challenges, something that becomes clearly evident in the start of World War II and Roosevelt's call for America to be "the arsenal of democracy."