Staying out of WWII was our foreign policy stance until Dec. 7, 1941. Sure, we had a lend/lease deal with Great Britain. But I'm not sure what our stance would have been had we not been attacked by the Japanese. Our Declaration of War on the Japanese meant that Germany and Italy declared war on the US, being their allies. We didn't start it, but we damned sure finished it. Our wartime defense manufacturing complex was the only one left standing, and it pulled the US out of The Great Depression.
Am I glad the US stepped in, absolutely. If the war had dragged on a few years longer, Germany would not have only had the best operational jet fighters, and the V2, it would also have had the atomic bomb, and thus would have been the first and only nuclear super power. If that would have happened, I would argue that there wouldn't have been less loss of life but more. Instead it ended up being the US, as that lone super power, and what we wanted was for the war to end. Luckily, our German engineers were better than the Russian's engineers until 1949.