Question

Why America should not have remained neutral in the Second world war?

Answer 1

If America remained neutral, it's possible the Axis forces of Germany, Japan, and Italy may have emerged as the reigning superpowers of their day. They could have won their respective theaters, but it also means that they didn't cross certain lines that would have made neutrality...and their own victories...impossible.

It's possible that Japan would have dominated the Pacific if America remained neutral provided they didn't attack Pearl Harbor. There would have been no one to really oppose them. Isolationism was strong in America at the time and many people did not want the US to get involved in another foreign war. Japan then could have focused on China and, perhaps, the Soviet Union as part of the Axis.

It's a little murkier with Germany. If the US didn't come to the aid of Britain and stayed out of the war, and if Hitler didn't declare war on the US after Pearl Harbor, then Britain would have been effectively isolated. There would be no Operation Torch in Africa to help crush Rommel, no D-Day landings, no Sicilian landings, nothing to take the Third Reich further off balance.

Germany could have then won the war, or at least force a decisive victory over the Soviets that could have forced them to capitulate, by focusing everything in their direction. Moscow could have been seized, and Stalin with it, though maintaining control of such a vast country would have been something of a different story. Remember, one of Hitler's driving motivations was racial purity. Quite a number of areas liberated by his armies from the Soviet Union celebrated their arrival because they hated Stalin and the Soviets. If he had worked with them instead of wanting to enslave and exterminate them because the Nazis believed they were inferior people, things might have gone much differently.