After the arrival of a transport at the ramp in Birkenau, the process known as selection took place. SS officers decided who would be taken to work, and who would be sent directly to the gas chambers. Often it was mere chance or the mood of the SS officer that decided whether someone died immediately or had a hope of survival. The prisoners selected for slave labour were sent to one of the many auxiliary camps at Auschwitz or elsewhere in the Nazi concentration camp system. Their aim was „Vernichtung durch Arbeit“ - extermination through labour.
In the first phase of World War II in Europe, Germany sought to avoid a long war. Germany's strategy was to defeat its opponents in a series of short campaigns. Germany quickly overran much of Europe and was victorious for more than two years by relying on a new military tactic called the "Blitzkrieg" (lightning war). Blitzkrieg tactics required the concentration of offensive weapons (such as tanks, planes, and artillery) along a narrow front. These forces would drive a breach in enemy defenses, permitting armored tank divisions to penetrate rapidly and roam freely behind enemy lines, causing shock and disorganization among the enemy defenses. German air power prevented the enemy from adequately resupplying or redeploying forces and thereby from sending reinforcements to seal breaches in the front. German forces could in turn encircle opposing troops and force surrender.
Throughout the 1930s, the legal, economic, and social rights of Jews were steadily restricted. On 1 April 1933, there was a boycott of Jewish businesses. On 7 April 1933, the Law for the Restoration of the Professional Civil Service was passed, which excluded Jews and other "non-Aryans" from the civil service. Jews were disbarred from practising law, being editors or proprietors of newspapers, joining the Journalists' Association, or owning farms. In Silesia, in March 1933, a group of men entered the courthouse and beat up Jewish lawyers; Friedländer writes that, in Dresden, Jewish lawyers and judges were dragged out of courtrooms during trials. Jewish students were restricted by quotas from attending schools and universities. Jewish businesses were targeted for closure or "Aryanization", the forcible sale to Germans; of the approximately 50,000 Jewish-owned businesses in Germany in 1933, about 7,000 were still Jewish-owned in April 1939. Works by Jewish composers, authors, and artists were excluded from publications, performances, and exhibitions. Jewish doctors were dismissed or urged to resign. The Deutsches Ärzteblatt (a medical journal) reported on 6 April 1933: "Germans are to be treated by Germans only."
During the Holocaust, concentration camp prisoners received tattoos only at one location, Auschwitz. Incoming prisoners were assigned a camp serial number which was sewn to their prison uniforms. Only those prisoners selected for work were issued serial numbers; those prisoners sent directly to the gas chambers were not registered and received no tattoos.
Up to this point, though, Auschwitz-Birkenau accounted for “only” 11 percent of the victims of the “Final Solution.” In August 1942, however, construction began on four large-scale gassing facilities. It appears from the plans that the first two gas chambers were adapted from mortuaries which, with the huge crematoria attached to them, were initially intended to cope with mortalities amongst the slave labor force in the camp, now approaching 100,000 and subject to a horrifying death rate. But from the autumn of 1942, it seems clear that the SS planners and civilian contractors were intending to build a mass-murder plant.
From 1933 until 1938, most of the people held in concentration camps were political prisoners and people the Nazis labeled as "asocial." These included the disabled, the homeless, and the mentally ill. After Kristallnacht in 1938, the persecution of Jews became more organized. This led to the exponential increase in the number of Jews sent to concentration camps.
In January 1945, as the Soviet army entered Krakow, the Germans ordered that Auschwitz be abandoned. Before the end of the month, in what came to be known as the Auschwitz death marches, an estimated 60,000 detainees, accompanied by Nazi guards, departed the camp and were forced to march to the Polish towns of Gliwice or Wodzislaw, some 30 miles away. Countless prisoners died during this process; those who made it to the sites were sent on trains to concentration camps in Germany.
For the first time, camps were created specifically for Jews. Their conditions were far worse than other camps. The implicit intention was that the inmates would die there. Increasing numbers of Jews in Poland were relocated in ghettos. Non-Jewish Poles were also deported from their farms and villages to make room for ‘pure’ ethnic Germans to populate the new territory.
Blitzkrieg would not have been possible without modifying Germany's standing interwar military, which under the Treaty of Versailles was limited to 100,000 men, its air force disbanded, and tank development forbidden. After becoming head of state in 1933, Adolf Hitler ignored these provisions. A command for armored troops was created within the German Wehrmacht—the Panzertruppe, as it came to be known later. The Luftwaffe, or air force, was re-established, and development begun on ground-attack aircraft and doctrines. Hitler was a strong supporter of this new strategy. He read Guderian's book Achtung! Panzer! and upon observing armored field exercises at Kummersdorf he remarked "That is what I want—and that is what I will have."