During World War II, ghettos were established by the Nazis to confine Jews, Romani and Serbs into tightly packed areas of the cities of Eastern Europe. Starting in 1939, the Nazis began to systematically move Polish Jews into designated areas of large Polish cities. The first large ghetto at Tuliszków was established in December 1939 or January 1940, followed by the Łódź Ghetto in April 1940 and the Warsaw Ghetto in October 1940, with many other ghettos established throughout 1940 and 1941. The ghettos were walled off, and any Jew found leaving them was shot. The Warsaw Ghetto was the largest of these ghettos, with 380,000 people and the Łódź Ghetto, the second largest, holding about 160,000.
The situation in the ghettos was brutal. In Warsaw, 30% of the population were forced to live in 2.4% of the city's area, a density of 9.2 people per room. In the ghetto of Odrzywół, 700 people lived in an area previously occupied by 5 families, between 12 and 30 to each small room. The Jews were not allowed out of the ghetto, so they had to rely on food supplied by the Nazis: in Warsaw this was 253 calories (1,060 kJ) per Jew, compared to 669 calories (2,800 kJ) per Pole and 2,613 calories (10,940 kJ) per German. With crowded living conditions, starvation diets, and little sanitation (in the Łódź Ghetto 95% of apartments had no sanitation, piped water or sewers) hundreds of thousands of Jews died of disease and starvation.
In 1942, the Nazis began Operation Reinhard, the systematic deportation to extermination camps during the Holocaust. The authorities deported Jews from everywhere in Europe to the ghettos of the East, or directly to the extermination camps -- almost 300,000 people were deported from the Warsaw Ghetto alone to Treblinka over the course of 52 days. In some of the Ghettos the local resistance organisations started ghetto uprisings. None were successful, and the Jewish populations of the ghettos were almost entirely killed.