The governments of the German Empire and Nazi Germany ordered, organized, and condoned a substantial number of war crimes, first in the Herero and Namaqua genocide and then in the First and Second World Wars. The most notable of these is the Holocaust, in which millions of European Jewish, Polish, and Romani people were systematically abused, deported, and murdered. Millions of civilians and prisoners of war also died as a result of German abuses, mistreatment, and deliberate starvation policies in those two conflicts. Much of the evidence was deliberately destroyed by the perpetrators, such as in Sonderaktion 1005, in an attempt to conceal their crimes.

The bombing of Wieluń is considered by many to be the first major act of World War II, and the September Campaign. After Luftwaffe air units moved into Polish airspace in the early morning of 1 September, they reached the town of Wieluń by 04:40–45. Around this time, the first strikes on the town were conducted, with a total of 46,000 kg bombs being dropped on civilian targets for 9 consecutive hours. Elsewhere, the Battle of Westerplatte and Danzig skirmishes began around the same time (04:45), starting the well-coordinated Invasion of Poland.