In the summer of 1941, the Nazis began implementing their 'Final Solution' plan to exterminate the Jews of Europe. Following the Wannsee Conference in January of 1942, the Nazis sped up their 'Final Solution' to exterminate the Jews of Europe. Operation Reinhard. 

To facilitate this, the Nazis established six extermination camps in occupied Poland: Chelmno, Majdanek, Treblinka, Sobibor, Belzec and Auschwitz-Birkenau. By the time of the Wannsee Conference, Chelmo was already fully operational, while the construction of Belzec was almost completed. While each camp was integral to carrying out the 'Final Solution', over time the method of murder was modified to make it more efficient.

Gas chambers were built and disguised as shower blocks at all of the camps except Chelmno, where mobile vans were crudely utilized to gas their victims with carbon-monoxide.

At Majdanek and Auschwitz-Birkenau selection took place, where some Jews were chosen to work as slave labourers producing goods for the Nazis. Chelmno, Treblinka, Sobibor and Belzec were built with the sole function to murder.

These four camps only existed for short periods of time and were then destroyed as the Nazis tried to cover up the evidence of their crimes.