As discrimination against Jews increased, German law required a legal definition of a Jew and an Aryan. Promulgated at the annual Nazi Party rally in Nürnberg on September 15, 1935, the Nürnberg Laws—the Law for the Protection of German Blood and German Honour and the Law of the Reich Citizen—became the centrepiece of anti-Jewish legislation and a precedent for defining and categorizing Jews in all German-controlled lands. Marriage and sexual relations between Jews and citizens of “German or kindred blood” were prohibited. Only “racial” Germans were entitled to civil and political rights. Jews were reduced to subjects of the state. The Nürnberg Laws formally divided Germans and Jews, yet neither the word German nor the word Jew was defined. That task was left to the bureaucracy. Two basic categories were established in November: Jews, those with at least three Jewish grandparents; and Mischlinge (“mongrels,” or “mixed breeds”), people with one or two Jewish grandparents. Thus, the definition of a Jew was primarily based not on the identity an individual affirmed or the religion he or she practiced but on his or her ancestry. Categorization was the first stage of destruction.
In the immediate postwar period, Mengele was in US custody. Unaware that Mengele's name already stood on a list of wanted war criminals, US officials quickly released him. From the summer of 1945 until spring 1949, using false papers, Mengele worked as a farmhand near Rosenheim, Bavaria. His prosperous family then aided his emigration to South America. He settled in Argentina.
In his 1965 essay "Command and Compliance", which originated in his work as an expert witness for the prosecution at the Frankfurt Auschwitz Trials, the German historian Hans Buchheim wrote there was no coercion to murder Jews and others, and all who committed such actions did so out of free will. Buchheim wrote that chances to avoid executing criminal orders "were both more numerous and more real than those concerned are generally prepared to admit",[468] and that he found no evidence that SS men who refused to carry out criminal orders were sent to concentration camps or executed.[469] Moreover, SS rules prohibited acts of gratuitous sadism, as Himmler wished for his men to remain "decent"; acts of sadism were carried out on the initiative of those who were either especially cruel or wished to prove themselves ardent National Socialists.[468] Finally, he argued that those of a non-criminal bent who committed crimes did so because they wished to conform to the values of the group they had joined and were afraid of being branded "weak" by their colleagues if they refused.[470]

On October 23, 1941, S.S. head Heinrich Himmler issued an order down the Nazi chain of command which heralded a major change in Nazi policy with respect to the “Jewish problem.” Until then, the Nazis worked vigorously to encourage Jews to emigrate. The Madagascar Plan (see below) was one example of strategies which were formulated to remove Jews from Germany and its occupied lands. As is described in more detail in Chapter 11, many countries refused to accept Jewish refugees. This shift in policy resulted in the deportation of Jews to camps and ghettos in the East. The policy to “resettle” Jews to these ghettos and camps was a significant step in what was to become the “Final Solution” the systematic murder of millions of Jews.

The ideology of Nazism brought together elements of antisemitism, racial hygiene, and eugenics, and combined them with pan-Germanism and territorial expansionism with the goal of obtaining more Lebensraum (living space) for the Germanic people.[16] Nazi Germany attempted to obtain this new territory by attacking Poland and the Soviet Union, intending to deport or kill the Jews and Slavs living there, who were considered by the Nazis to be inferior to the Aryan master race.[17]