The Holocaust: The gas chambers at Treblinka extermination camp began operation, killing 6,500 Jews who had been transported from the Warsaw Ghetto the day before.

The Holocaust, known in Hebrew as the Shoah, was the genocide of European Jews during World War II. From 1941 to 1945, Nazi Germany and its collaborators systematically murdered some six million Jews across German-occupied Europe, around two-thirds of Europe's Jewish population. The murders were committed primarily through mass shootings across Eastern Europe and poison gas chambers in extermination camps, chiefly Auschwitz-Birkenau, Treblinka, Belzec, Sobibor, and Chełmno in occupied Poland. Separate Nazi persecutions killed millions of other non-Jewish civilians and prisoners of war (POWs); the term Holocaust is sometimes used to include the murder and persecution of non-Jewish groups.

A gas chamber is an apparatus for killing humans or animals with gas, consisting of a sealed chamber into which a poisonous or asphyxiant gas is introduced. Poisonous agents used include hydrogen cyanide and carbon monoxide.

Treblinka was the second-deadliest extermination camp to be built and operated by Nazi Germany in occupied Poland during World War II. It was in a forest north-east of Warsaw, four kilometres south of the village of Treblinka in what is now the Masovian Voivodeship. The camp operated between 23 July 1942 and 19 October 1943 as part of Operation Reinhard, the deadliest phase of the Final Solution. During this time, it is estimated that between 700,000 and 900,000 Jews were murdered in its gas chambers, along with 2,000 Romani people. More Jews were murdered at Treblinka than at any other Nazi extermination camp apart from Auschwitz-Birkenau.

The Warsaw Ghetto was the largest of the Nazi ghettos during World War II and the Holocaust. It was established in November 1940 by the German authorities within the new General Government territory of occupied Poland. At its height, as many as 460,000 Jews were imprisoned there, in an area of 3.4 km² (1.3 sq mi), with an average of 9.2 persons per room, barely subsisting on meager food rations. Jews were deported from the Warsaw Ghetto to Nazi concentration camps and mass-killing centers. In the summer of 1942, at least 254,000 ghetto residents were sent to the Treblinka extermination camp during Großaktion Warschau under the guise of "resettlement in the East" over the course of the summer. The ghetto was demolished by the Germans in May 1943 after the Warsaw Ghetto Uprising had temporarily halted the deportations. The total death toll among the prisoners of the ghetto is estimated to be at least 300,000 killed by bullet or gas, combined with 92,000 victims of starvation and related diseases, the Warsaw Ghetto Uprising, and the casualties of the final destruction of the ghetto.