Poland had not existed since the 18th century. After WWI it was reconstituted out land taken from Germany and Russia. As far as the Russians were concerned, they were getting some of their own back. I’m not saying it was right, just that they saw it that way (sorta like the Chinese believing that every land that ever paid them tribute is actually a stray part of “Greater China” or something like that...).
If we wanted to fight Germany, we had to collude with the Soviets. There was an example of the Russians signing a separate peace with Germany in WWI. If the Russians had signed a separate peace in WWII, the Germans would have been able to double the forces facing us. If didn’t want to fight Germany, well, we were not offered that choice.
Hitler and Stalin both signed the Non-Aggression Pact assuming certain things would happen, that didn’t turn out for them.
Stalin expected a long protacted war in the West, which would deplete the armies of Britain, France and Germany, allowing the Soviets to swoop in and conquer all of Europe.....but what he didn’t count on was France falling in just six weeks.
Hitler thought the Non-Aggression Pact would get Britain and France to call off the dogs, and give him free rein in Eastern Europe, which also didn’t happen.
Hitler was obsessed with eliminating every single Jew on the planet....certainly conquering the US and eliminating her Jews was going to be something Hitler would do, if he was in position to do so.
“As far as the Russians were concerned, they were getting some of their own back.”
Germany (and Austria) used the same logic; Poland was re-created from territory of all three after WWI. That same defense could be used by the USSR for keeping the Baltic states (and trying for Finland); all four were created from Tsarist Russian territory.
“If we wanted to fight Germany, we had to collude with the Soviets.”
As with WWI, we had little reason to fight Germany. In any case, Germany achieved its goal (domination of Europe) and the views held by the Nazis (post-Christian paganism) also dominate.