From a Marxist perspective, UK, USA, France etc had the same class interests as Nazi Germany. They were also uncomfortably okay with the Nazis Pre-war. I know this is a big topic (and I’m sure some marxist books have been written on it) but briefly why did the Allies fight against Nazi Germany from a dialectical pov.
United Kingdom: Considered itself as the sole nation to have the divine right to divide and conquer and any nation on the planet and declares otherwise is UK’s enemy. A united Europe would makes the UK look like Japan to China.
France: It’s biggest friend during World War I was the Russian Empire, but since Russian revolution killing the royal family and replacing the Empire with the Soviet Union, France lost it’s biggest friend.
So then they then looked at an aggressive Poland who took use of the Russian civil war and invaded large parts Lithuania, Belarus and Ukraine and decided they wanted to Poland to be their new best friend and signed military alliance treaty.
Around 15 years later Poland got invaded by Germany.
United States: Did not join World War 2, but got attacked by Japan.