Hmmm...you mean the war that Roosevelt's socialist party may have been a significant CAUSE?
Keep in mind that the American boom in the Roaring Twenties was due to our first major expansion to our capitalist, middle-class industrial society. FDR took a recession that, although serious, had not been disastrous, and used it as an excuse to implement socialistic policies that destroyed any capitalist advances gained.
Keep in mind that our trade was not just based upon domestic policies, but our rapidly expanding international trade was the first major casualty. It is no coincidence that Japan and post-WW1 continental Europe were among our biggest trade partners in the 20's. When FDR socialized the economy in the 30's, he not only created a decade-long depression, he also stifled trade with two areas of the world that resulted in an infestation economic malaise, which allowed Imperial Japan and the Wiemar Republic to aggressively pursue their military agendas...which turned into the biggest world war in history.
To that end, FDR's involvement has heretofore never been questioned, but economics play the biggest role in determining country fates. Socialist policies lead to war, capitalist policies lead to peace. There cannot be any other result based upon human nature.