In September 1939, Nazi Germany invaded Poland, starting the Second World War. As Germany conquered more territory, millions of Jews fell under Nazi control. The Nazis extended their anti-Jewish laws to these new territories. But their ultimate goal was to make these lands Judenfrei, or free of Jews. 

A key step in this process was the creation of Jewish ghettos. Ghettos were segregated areas set up in the worst parts of town. The ghettos were usually enclosed by walls or barbed wire to isolate Jews from the rest of society. The Nazis established over 1,000 ghettos, mostly in Eastern Europe. Jews from across eastern Europe were rounded up from their homes and forced into ghettos. The Nazis saw this as a temporary solution to what they called "the Jewish problem." 

Ghettos were extremely overcrowded. There was little food, water, sanitation or medicine. As a result, starvation and disease caused the deaths of about 500,000 Jews in ghettos. Factories were set up in some ghettos to exploit Jewish labour before deporting them to death camps.  

The Nazis forced Jewish elders to run the ghettos and implement Nazi orders. The councils of Jewish elders tried to provide services for ghetto residents, but they could do little without access to food and medicine. The councils were also faced with impossible moral choices, like deciding who in the ghettos should be deported to the death camps. 

Despite the terrible conditions in the ghettos, Jews maintained their dignity. They organized hospitals, orphanages, secret schools and religious services. In hidden archives, Jews preserved evidence of life under Nazi rule. In some ghettos, Jews even fought back in armed revolts. The most famous of these was the Warsaw Ghetto Uprising in 1943.