Was entering WWII a mistake?

[Cory]

No. There's no telling how much better the world would be if the USA somehow entered the war in September of 1939.

[Cory]

As for if we should have jumped in earlier, it's a tricky question. Clearly, there was a moral imperative to destroy Nazi Germany as soon as it became clear how evil they were. However, there was a growing, powerful fascist movement in the US harnessing post-WW1/Depression isolationism effectively, and an unpopular entry into the war before we were attacked could have galvanized them.

You use the word "powerful" rather liberally.

Spoiler alert: If America enters the war in 1939 France doesn't fall and Germany is defeated by the end of 1941. Italy remains neutral however.

Not joining the League of Nations is probably the singe most disastrous foreign policy decision undertaken by the USA in the 20th Century.

[Cory]

Nahh, even with an American Force France is going down.

Nothing can save France in 1940

Nonsense. The Germany victory in Western Europe in 1940 was a very close run thing. The capability of the French military in 1939/40 is highly underrated.

Sickle Cut was a shot in the dark, a massive gamble that required everything to go right.

[Cory]

After the Soviet Union was attacked we could've got away with only fighting Japan, as Stalin had far more reserves, far more front-line troops etc. He still would've gotten to Berlin, and quite possibly on the same time frame if we keep supplying him with tanks, planes etc. (And keep in mind Operation Barbarossa was about 5 and a half months before the bombing of Pearl Harbor).

I highly, highly doubt that. Without American entry there would be almost zero threat of a second front on mainland Europe and thusly Germany could free up more men and material to go to the East. Not to mention that German morale would be higher, there would no major strategic bombing campaign, and lend-lease to the USSR will be a tough sell to Congress without America at war with Germany.

The Soviets may well still win the war, but the idea that it would be on the same time-frame and everything will be fine is nonsense. Also consider that without any serious invasion of Western/Southern Europe the Soviets will gain much more of Europe then in actual history. The British won't be able to invade until after basically the entire German military has already been decimated by the Soviets.

A yeah, not going to war with Germany would've basically been a major strategic miscalculation at best.