Answer:
After Germany invaded the Soviet Union in June 1941, several million more Jews came under Nazi rule. The Germans aimed to control this sizable Jewish population by forcing Jews to reside in marked-off sections of towns and cities the Nazis called "ghettos" or "Jewish residential quarters." Altogether, the Germans created at least 1,000 ghettos in occupied territories. The largest ghetto was in Warsaw, the Polish capital, where almost half a million Jews were confined.
I learned this because I’m Jewish and my father taught me because he wants me to know the history. lol