Jews, Gypsies (Roma), homosexuals, asocials, criminals, and prisoners of war were gathered, stuffed into cattle cars on trains, and sent to Auschwitz. When the trains stopped at Auschwitz II: Birkenau, the newly arrived were told to leave all their belongings on board and were then forced to disembark from the train and gather upon the railway platform, known as "the ramp."
Auschwitz-Birkenau was also a killing center and played a central role in the German effort to kill the Jews of Europe. Around the beginning of September, 1941, the SS at Auschwitz I conducted the first tests of Zyklon B as a mass murder agent, using Soviet POWs and debilitated Polish prisoners as victims. The “success” of these experiments led to the construction of a chamber in the crematorium of Auschwitz I that, like the subsequent gas chambers at Auschwitz, used Zyklon B to murder victims. The first transports of Jewish men, women, and children sent to Auschwitz as part of the “final solution” were murdered in this gas chamber (Crematorium I) in February and March 1942.
The concept of the Aryan race, which the Nazis promoted, stems from racial theories asserting that Europeans are the descendants of Indo-Iranian settlers, people of ancient India and ancient Persia.[80] Proponents of this theory based their assertion on the fact that words in European languages and words in Indo-Iranian languages have similar pronunciations and meanings.[80] Johann Gottfried Herder argued that the Germanic peoples held close racial connections to the ancient Indians and the ancient Persians, who he claimed were advanced peoples that possessed a great capacity for wisdom, nobility, restraint and science.[80] Contemporaries of Herder used the concept of the Aryan race to draw a distinction between what they deemed to be "high and noble" Aryan culture versus that of "parasitic" Semitic culture.[80]

The Nazi Party's precursor, the Pan-German nationalist and antisemitic German Workers' Party, was founded on 5 January 1919. By the early 1920s the party was renamed the National Socialist German Workers' Party – to attract workers away from left-wing parties such as the Social Democrats (SPD) and the Communists (KPD) – and Adolf Hitler assumed control of the organization. The National Socialist Program or "25 Points" was adopted in 1920 and called for a united Greater Germany that would deny citizenship to Jews or those of Jewish descent, while also supporting land reform and the nationalization of some industries. In Mein Kampf ("My Struggle"; 1924–1925), Hitler outlined the anti-Semitism and anti-Communism at the heart of his political philosophy, as well as his disdain for representative democracy and his belief in Germany's right to territorial expansion.[5]
While no unified resistance movement opposing the Nazi regime existed, acts of defiance such as sabotage and labour slowdowns took place, as well as attempts to overthrow the regime or assassinate Hitler.[435] The banned Communist and Social Democratic parties set up resistance networks in the mid-1930s. These networks achieved little beyond fomenting unrest and initiating short-lived strikes.[436] Carl Friedrich Goerdeler, who initially supported Hitler, changed his mind in 1936 and was later a participant in the July 20 plot.[437][438] The Red Orchestra spy ring provided information to the Allies about Nazi war crimes, helped orchestrate escapes from Germany, and distributed leaflets. The group was detected by the Gestapo and more than 50 members were tried and executed in 1942.[439] Communist and Social Democratic resistance groups resumed activity in late 1942, but were unable to achieve much beyond distributing leaflets. The two groups saw themselves as potential rival parties in post-war Germany, and for the most part did not co-ordinate their activities.[440] The White Rose resistance group was primarily active in 1942–43, and many of its members were arrested or executed, with the final arrests taking place in 1944.[441] Another civilian resistance group, the Kreisau Circle, had some connections with the military conspirators, and many of its members were arrested after the failed 20 July plot.[442]
In the Holocaust, millions of Jews, as well as Roma people (also called "Gypsies"), people with disabilities, homosexuals, political opponents, and many other people were sent to concentration camps and death camps in Poland and Germany. The Nazis killed millions of these people at the concentration camps with poison gas. The Nazis also killed millions of people in these groups by forcing them to do slave labor without giving them much food or clothing. In total, 17 million people died- 6 million of them Jews.
Long before the Nazis took power, concentration camps had featured in their imagination. Wachsmann finds Hitler threatening to put Jews in camps as early as 1921. But there were no detailed plans for building such camps when Hitler was named Chancellor of Germany, in January, 1933. A few weeks later, on February 27th, he seized on the burning of the Reichstag—by Communists, he alleged—to launch a full-scale crackdown on his political opponents. The next day, he implemented a decree, “For the Protection of People and State,” that authorized the government to place just about anyone in “protective custody,” a euphemism for indefinite detention. (Euphemism, too, was to be a durable feature of the K.L. universe: the killing of prisoners was referred to as Sonderbehandlung, “special treatment.”)

Remarkably, there were instances of individual resistance and collective efforts at fighting back inside Auschwitz. Poles, Communists and other national groups established networks in the main camp. Some Jews assaulted Nazi guards, even at the entrance to the gas chambers. In October 1944, the Sonderkommando crew at crematoria IV revolted and destroyed the crematoria. It was never used again.
According to the numbers provided by the US Holocaust Memorial Museum, Auschwitz was the site of the most deaths (1.1 million) of any of the six dedicated extermination camps. By these estimates, Auschwitz was the site of at least one out of every six deaths during the Holocaust. The only camp with comparable figures was Treblinka in north-east Poland, where about 850,000 are thought to have died.
Hitler’s intellectual viewpoint was influenced during his youth not only by these currents in the German tradition but also by specific Austrian movements that professed various political sentiments, notably those of pan-Germanic expansionism and anti-Semitism. Hitler’s ferocious nationalism, his contempt of the Slavs, and his hatred of the Jews can largely be explained by his bitter experiences as an unsuccessful artist living a threadbare existence on the streets of Vienna, the capital of the multiethnic Austro-Hungarian Empire.
Against the advice of many of his senior military officers, Hitler ordered an attack on France and the Low Countries, which began in May 1940.[97][98] They quickly conquered Luxembourg and the Netherlands. After outmanoeuvring the Allies in Belgium and forcing the evacuation of many British and French troops at Dunkirk,[99] France fell as well, surrendering to Germany on 22 June.[100] The victory in France resulted in an upswing in Hitler's popularity and an upsurge in war fever in Germany.[101]
The Soviet occupation of eastern Poland in 1939 and the absorption of the Baltic states in 1940 led to the incarceration of large numbers of non-Soviet citizens. Following the outbreak of war with Germany in 1941, the camps received Axis prisoners of war and Soviet nationals accused of collaboration with the enemy. After the death of Joseph Stalin in 1953, many prisoners were released and the number of camps was drastically reduced. See also Gulag.

The first party that attempted to combine nationalism and socialism was the (Austria-Hungary) German Workers' Party, which predominantly aimed to solve the conflict between the Austrian Germans and the Czechs in the multi-ethnic Austrian Empire, then part of Austria-Hungary.[70] In 1896 the German politician Friedrich Naumann formed the National-Social Association which aimed to combine German nationalism and a non-Marxist form of socialism together; the attempt turned out to be futile and the idea of linking nationalism with socialism quickly became equated with antisemites, extreme German nationalists and the Völkisch movement in general.[27]
In most camps, prisoners were forced to wear identifying overalls with colored badges according to their categorization: red triangles for Communists and other political prisoners, green triangles for common criminals, pink triangles for homosexual men, purple triangles for Jehovah's Witnesses, black triangles for asocials and the "work shy", yellow triangle for Jews, and later the brown triangle for Romanis.[30]