During World War II, German forces, with the aid of local Ukrainian collaborators, begin the two-day Babi Yar massacre.

World War II or the Second World War was a global conflict between two coalitions: the Allies and the Axis powers. Nearly all of the world's countries participated, with many nations mobilising all resources in pursuit of total war. Tanks and aircraft played major roles, enabling the strategic bombing of cities and delivery of the first and only nuclear weapons ever used in war. World War II is the deadliest conflict in history, causing the death of 70 to 85 million people, more than half of whom were civilians. Millions died in genocides, including the Holocaust, and by massacres, starvation, and disease. After the Allied victory, Germany, Austria, Japan, and Korea were occupied, and German and Japanese leaders were tried for war crimes.

Nazi Germany, officially the German Reich and later the Greater German Reich, was the German state between 1933 and 1945, when Adolf Hitler and the Nazi Party controlled the country, transforming it into a totalitarian dictatorship. The Third Reich, meaning "Third Realm" or "Third Empire", referred to the Nazi claim that Nazi Germany was the successor to the earlier Holy Roman Empire (800–1806) and German Empire (1871–1918). The Third Reich, which the Nazis referred to as the Thousand-Year Reich, ended in May 1945, after 12 years, when the Allies defeated Germany and entered the capital, Berlin, ending World War II in Europe.

Ukrainian collaboration with Nazi Germany took place during the occupation of Poland and the Ukrainian SSR, USSR, by Nazi Germany during the Second World War.

Babi Yar or Babyn Yar is a ravine in the Ukrainian capital Kyiv and a site of massacres carried out by Nazi Germany's forces during its campaign against the Soviet Union in World War II. The first and best documented of the massacres took place on 29–30 September 1941, in which some 33,771 Jews were murdered. Other victims of massacres at the site included Soviet prisoners of war, communists and Romani people. It is estimated that a total of between 100,000 and 150,000 people were murdered at Babi Yar during the German occupation.