They had an absolute lack of appetite for fighting since the WWI was not long ago. I don't know if the Germans were smart enough to understand that and fully took advantage of it or were just lucky. For the Germans it worked with Czechoslovakia so they figured it would work with Poland as well.

Stalin I think is more interesting. He was prepared to "defend" the Czechs as well. He just needed permission to take his armies across Poland and Romania. He quickly switched sides after the agreement and signed the Soviet-German agreement.

Not too long ago I also learned about the secret military cooperation between the Soviets and the Germans https://en.wikipedia.org/wiki/Germany%E2%80%93Soviet_Union_r.... The German air force was training its pilots in the Soviet Union:

> In 1925, a flying school was established near Lipetsk (Lipetsk fighter-pilot school) to train the first pilots for the future Luftwaffe

Reading that it's like reading some alternative universe fan-fiction. So that makes Stalin's position interesting. He was supposed to be allied with the French and the British officially but non-officially was assisting the Germans.