Yugoslavia and Greece were invaded in April 1941 and surrendered before the end of the month. Germany and Italy divided Greece into occupation zones but did not eliminate it as a country. Yugoslavia, home to around 80,000 Jews, was dismembered; regions in the north were annexed by Germany and regions along the coast made part of Italy. The rest of the country was divided into the Independent State of Croatia, nominally an ally of Germany, and Serbia, which was governed by a combination of military and police administrators. According to historian Jeremy Black, Serbia was declared free of Jews in August 1942. Croatia's ruling party, the Ustashe, killed the country's Jews, and killed or expelled Orthodox Christian Serbs and Muslims. Jews and Serbs alike were "hacked to death and burned in barns", according to Black. One difference between the Germans and Croatians was that the Ustashe allowed its Jewish and Serbian victims to convert to Catholicism so they could escape death.
In the final months of the war, SS guards moved camp inmates by train or on forced marches, often called “death marches,” in an attempt to prevent the Allied liberation of large numbers of prisoners. As Allied forces moved across Europe in a series of offensives against Germany, they began to encounter and liberate concentration camp prisoners, as well as prisoners en route by forced march from one camp to another. The marches continued until May 7, 1945, the day the German armed forces surrendered unconditionally to the Allies.
The German skill in adapting the 20th century techniques of mass production was applied in engineering the “Final Solution.” In 1941, the engineers of the “Final Solution” utilized these same principles to cheaply and efficiently murder millions of Jews and other “undesirables.” The plants established to carry out this mass murder were the death camps.
The number of Afro-Germans in Germany when the Nazis came to power is variously estimated at 5,000–25,000. It is not clear whether these figures included Asians. Although blacks, including prisoners of war, in Germany and German-occupied Europe were subjected to incarceration, sterilization, murder, and other abuse, there was no programme to kill them all as there was for the Jews.
Before the war, Mengele had received doctorates in anthropology and medicine, and began a career as a researcher. He joined the Nazi Party in 1937 and the SS in 1938. He was assigned as a battalion medical officer at the start of World War II, then transferred to the Nazi concentration camps service in early 1943 and assigned to Auschwitz, where he saw the opportunity to conduct genetic research on human subjects. His subsequent experiments focused primarily on twins, with little regard for the health or safety of the victims.