1939, Nazis experimented with poison gas
In 1942, systematic mass killing in stationary gas chambers (with carbon monoxide gas generated by diesel engines) began at Belzec, Sobibor, and Treblinka, all in Poland.
Nazis choose the town of Oswiecim (Auschwitz) in Poland near Krakow as the site of a new concentration camp.
Paris is occupied by the Nazis.
Nazis invade Russia.
Jews in France, Holland, Belgium, Croatia, Slovakia, Romania ordered to wear yellow stars.