Plans to isolate the Jewish population of Warsaw and its nearby suburbs in a ghetto first circulated immediately after the German occupation of Poland in 1939. At the time, the German administration of the General Government had not been fully organized, and there were conflicting interests among the three major players: the civilian administration, the military, and the SS. Under these circumstances, the Jewish Council, or Judenrat, headed by Adam Czerniaków, was able to delay the establishment of the Ghetto by one year, mainly by appealing to the military to consider how Jews were a valuable labor resource. The Jewish were rounded up and allocated a scrubby flat and given little food.
The Warsaw Ghetto was established by the German Governor-General Hans Frank on October 16, 1940. At this time, the population of the Ghetto was estimated to be 440,000 people, about 37% of the population of Warsaw. However, the size of the Ghetto was about 4.5% of the size of Warsaw. Nazis then closed off the Warsaw Ghetto from the outside world on November 16th that year, building a wall.
During the next year and a half, Jews and Roma people  from smaller cities and the countryside were brought into the Ghetto, while diseases (especially typhoid) and starvation kept the inhabitants at about the same number. Average food rations in 1941 for Jews in Warsaw were limited to 253 kcal, compared to 2,325 kcal for gentile Poles and 5,613 kcal for German people. The life in the ghetto was chronicled by the Oyneg Shabbos group. In 1942 Polish resistance fighter Jan Karski reported to the Western governments on the situation in the Ghetto and on the extermination camps.
Thousands of residents died due to rampant disease or starvation, as well as random killings, even before the Nazis began massive deportations of the inhabitants from the Ghetto's Umschlagplatz to the Treblinka extermination camp. In the 52 days before September 12, 1942, about 300,000 Ghetto residents were sent to the extermination camps and killed there. By the end of 1942, it was clear that the deportations were to their deaths, and many of the remaining Jews decided to fight.