My family visited Warsaw in 1999 when they had just opened a WWII museum downtown.
The history that they tell is that the death camps were originally built for Polish upper class before they were used for the Jews. The Germans intended to suppress anyone in Poland who exhibited leadership abilities leaving a slave class in place for the benefit of the Germans.
The museum also gives details of how the Germans and Russians invaded Poland in a pincer movement. The Germans came in by land from the west and the sea via Gdansk. The Soviets came by train within a short time from the east.
We were touring the museum with Polish college students. One of them said that their aunt and uncle had fled from the German invasion by getting on a train going east. At the Polish border, Russians were arriving as their train pulled into the station. So his aunt and uncle went back west to Warsaw. This college student said that his uncle was arrested and assigned as a farm laborer in northern Germany. The uncle said that the German farmer that he worked for treated him well and that he survived the war. I don’t remember what happened to his aunt.
Indeed. Soon after the occupation, they arrested all of the professors of Jagellonian University in Krakow and sent them to camps where many of them perished.