I don't know about the United States, but Britain, France, and other allied powers should have fought Hitler as early as 1936 when he was still weak rather than in 1939 when he invaded Poland when he was too strong to be defeated by either one of them.
Agreed. Letting conquerers gain strength until they become strong enough to defeat you is a stupid idea.
Though at the time, it wasn't really clear what was about to happen.
I wouldn't say that. The writing was on the wall, and Hitler kept breaking the clauses in the Versaille Treaty, so there was something of a Casus Belli present.
