Germany implemented the persecution of the Jews in stages. Following Adolf Hitler's appointment as German Chancellor in January 1933, the regime built a network of concentration camps in Germany for political opponents and those deemed "undesirable", starting with Dachau on 22 March 1933. After the passing of the Enabling Act on 24 March, which gave Hitler plenary powers, the government began isolating Jews from civil society, which included a boycott of Jewish businesses in April 1933 and enacting the Nuremberg Laws in September 1935. On 9–10 November 1938, during Kristallnacht (the "Night of Broken Glass"), Jewish businesses and other buildings were ransacked, smashed or set on fire throughout Germany and Austria, which Germany had annexed in March that year. After Germany invaded Poland in September 1939, triggering World War II, the regime set up ghettos to segregate Jews. Eventually thousands of camps and other detention sites were established across German-occupied Europe.
The Germans began World War II by invading Poland in September 1939. The Nazi leaders then shifted priorities in anti-Jewish policy from expulsion from German-controlled territory to concentration of European Jewish populations in locations suited to future permanent removal. It is not clear that the Nazi leaders were already envisioning mass murder as their "solution" to their so-called Jewish problem.
By the end of September, the SS had started to develop plans to deport Jews to newly invaded Poland: the first steps towards the systematic murder that would follow. In Poland itself, thousands of Poles and Jews were rounded up and shot, early indications of the systematic murder that would follow. Alongside this, Hitler approved a new programme of euthanasia to exterminate the handicapped and mentally ill.
In the first phase of the experiments, pairs of twins and persons with inherited anomalies were put at the disposal of Dr. Mengele and subjected to all imaginable specialist medical examinations. They were also photographed, plaster casts were made of their jaws and teeth, and they were toe- and fingerprinted. As soon as these examinations were finished, they were killed with lethal injections of phenol to the heart so that the next phase of the experimentation could begin: autopsies and the comparative analysis of their internal organs.
Racial-Morphological Examinations of the Anterior Portion of the Lower Jaw in Four Racial Groups. This dissertation, completed in 1935 and first published in 1937, earned him a PhD in anthropology from Munich University. In this work Mengele sought to demonstrate that there were structural differences in the lower jaws of individuals from different ethnic groups, and that racial distinctions could be made based on these differences.
Jews would be “utilised for work in the East… [The] sexes [will be] separated. Jews capable of work will be moved into these areas as they build roads, during which a large proportion will no doubt drop out through natural reduction. The remnant that eventually remains will require suitable treatment…The evacuated Jews will first be taken, group by group, to so-called transit ghettos, in order to be transported further east from there.”
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. 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.