From the mid- to late 1930s, Hitler undermined the postwar international order step by step. He withdrew Germany from the League of Nations in 1933, rebuilt German armed forces beyond what was permitted by the Treaty of Versailles, reoccupied the German Rhineland in 1936, annexed Austria in 1938 and invaded Czechoslovakia in 1939. When Nazi Germany moved toward Poland, Great Britain and France countered further aggression by guaranteeing Polish security. Nevertheless, Germany invaded Poland on September 1, 1939, and Great Britain and France declared war on Germany. Six years of Nazi Party foreign policy had ignited World War II.
The NSDAP (Nazi Party) assumed power in 1933 in the aftermath and decline of the Weimar Republic. In response to the instability created by the Great Depression, the Nazis sought a Third Way managed economy that was neither capitalism nor communism. Nazi rule effectively ended on May 7, 1945, V-E Day (Victory in Europe Day), when the Nazis unconditionally surrendered to the Allied Powers, who took over Germany's administration until Germany could form its own democratic government. 

Some of the conquered territories were incorporated into Germany as part of Hitler's long-term goal of creating a Greater Germanic Reich. Several areas, such as Alsace-Lorraine, were placed under the authority of an adjacent Gau (regional district). The Reichskommissariate (Reich Commissariats), quasi-colonial regimes, were established in some occupied countries. Areas placed under German administration included the Protectorate of Bohemia and Moravia, Reichskommissariat Ostland (encompassing the Baltic states and Belarus), and Reichskommissariat Ukraine. Conquered areas of Belgium and France were placed under control of the Military Administration in Belgium and Northern France.[167] Belgian Eupen-Malmedy, which had been part of Germany until 1919, was annexed. Part of Poland was incorporated into the Reich, and the General Government was established in occupied central Poland.[168] The governments of Denmark, Norway (Reichskommissariat Norwegen), and the Netherlands (Reichskommissariat Niederlande) were placed under civilian administrations staffed largely by natives.[167][g] Hitler intended to eventually incorporate many of these areas into the Reich.[169] Germany occupied the Italian protectorate of Albania and the Italian governorate of Montenegro in 1943[170] and installed a puppet government in occupied Serbia in 1941.[171]

Located in Nazi-occupied Poland, Auschwitz was the largest of all of the German Nazi concentration, forced labor, and extermination camps. More than 1.1 million people were murdered behind the barbed-wire fences of Auschwitz between May 1940 and January 1945. Around 1 million of those murdered were Jews, along with nearly 75,000 Poles, 21,000 Sinti and Roma, 14,000 Soviet prisoners of war, and nearly 15,000 others whom the Nazis deemed “inferior” or “undesirable” (including those who were allegedly homosexual, Jehovah’s Witnesses, and people the Nazis called criminals). Those kept as prisoners were stripped of their names, assigned numbers, and subjected to forced labor and brutal—frequently deadly—conditions.
A concentration camp to house Soviet prisoners of war and Poles had been established at Majdanek, close to the Polish city of Lublin, during 1941. In the spring of 1942 gas chambers and crematoria were added, turning Majdanek into an extermination camp that would murder 78,000 people. Auschwitz-Birkenau, the most infamous of the Nazi death camps, was a massive concentration, forced labour and extermination camp at the centre of a network of more than 40 satellite camps. Upwards of 80 per cent of those Jews transported to Auschwitz-Birkenau were selected for immediate death.
The crematoria consisted of a dressing room, gas chamber, and furnace room. In crematoria II and III, the dressing room and gas chamber were underground; in IV and V, they were on the ground floor. The dressing room had numbered hooks on the wall to hang clothes. In crematorium II, there was also a dissection room (Sezierraum).[172] SS officers told the victims they were to take a shower and undergo delousing. The victims undressed in the dressing room and walked into the gas chamber, which was disguised as a shower facility; signs in German said "To the baths" and "To disinfection". Some inmates were even given soap and a towel.[173]

There was one latrine for thirty to thirty-two thousand women and we were permitted to use it only at certain hours of the day. We stood in line to get in to this tiny building, knee-deep in human excrement. As we all suffered from dysentry, we could barely wait until our turn came, and soiled our ragged clothes, which never came off our bodies, thus adding to the horror of our existence by the terrible smell that surrounded us like a cloud. The latrine consisted of a deep ditch with planks thrown across it at certain intervals. We squatted on those planks like birds perched on a telegraph wire, so close together that we could not help soiling one another.[124]
The term "National Socialism" arose out of attempts to create a nationalist redefinition of "socialism", as an alternative to both international socialism and free market capitalism. Nazism rejected the Marxist concept of class conflict, opposed cosmopolitan internationalism, and sought to convince all parts of the new German society to subordinate their personal interests to the "common good", accepting political interests as the main priority of economic organization.[4]
The Reichstag fire on 27 February 1933 gave Hitler a pretext for suppressing his political opponents. The following day he persuaded the Reich's President Paul von Hindenburg to issue the Reichstag Fire Decree, which suspended most civil liberties. The NSDAP won the parliamentary election on 5 March 1933 with 43.9 percent of votes, but failed to win an absolute majority. After the election, hundreds of thousands of new members joined the party for opportunistic reasons, most of them civil servants and white-collar workers. They were nicknamed the "casualties of March" (German: Märzgefallenen) or "March violets" (German: Märzveilchen).[78] To protect the party from too many non-ideological turncoats who were viewed by the so-called "old fighters" (alte Kämpfer) with some mistrust,[79] the party issued a freeze on admissions that remained in force from May 1933 to 1937.[80]

Germany regained control of the Saarland through a referendum held in 1935 and annexed Austria in the Anschluss of 1938.[164] The Munich Agreement of 1938 gave Germany control of the Sudetenland, and they seized the remainder of Czechoslovakia six months later.[70] Under threat of invasion by sea, Lithuania surrendered the Memel district in March 1939.[165]
After the Night of the Long Knives, Hitler promoted Himmler and the SS, who then zealously suppressed homosexuality by saying: "We must exterminate these people root and branch ... the homosexual must be eliminated".[201] In 1936, Himmler established the "Reichszentrale zur Bekämpfung der Homosexualität und Abtreibung" ("Reich Central Office for the Combating of Homosexuality and Abortion").[202] The Nazi regime incarcerated some 100,000 homosexuals during the 1930s.[203] As concentration camp prisoners, homosexual men were forced to wear pink triangle badges.[204][205] Nazi ideology still viewed German men who were gay as a part of the Aryan master race, but the Nazi regime attempted to force them into sexual and social conformity. Homosexuals were viewed as failing in their duty to procreate and reproduce for the Aryan nation. Gay men who would not change or feign a change in their sexual orientation were sent to concentration camps under the "Extermination Through Work" campaign.[206]
The hair of 12 year-old Lili had not been cut since her early childhood. When she and her family were forced to leave their home in Târgu-Mureş and move to the ghetto, Lili’s mother, Rivka, knew she would not be able to care properly for her daughter’s hair in the ghetto. Chopping off Lili’s two long, beautiful braids, she promised that they would be given to the neighbors for safekeeping.Within six weeks, Lili and her mother were murdered at Auschwitz.
Nazism’s principal instrument of control was the unification, under Heinrich Himmler and his chief lieutenant, Reinhard Heydrich, of the SS (the uniformed police force of the Nazi Party) and all other police and security organizations. Opposition to the regime was destroyed either by outright terror or, more frequently, by the all-pervading fear of possible repression. Opponents of the regime were branded enemies of the state and of the people, and an elaborate web of informers—often members of the family or intimate friends—imposed utmost caution on all expressions and activities. Justice was no longer recognized as objective but was completely subordinated to the alleged needs and interests of the Volk. In addition to the now-debased methods of the normal judicial process, special detention camps were erected. In these camps the SS exercised supreme authority and introduced a system of sadistic brutality unrivaled in modern times.

That Mengele – they call him a doctor, but he was as much a doctor as I’m an army general. A complete fake of a man who I was too scared to look in the eye. I saw him day in, day out for months and was one of 152 Jews in his “care”. One of the experiments he carried out on me was to take blood from my arm and inject it in my rear end. I’ve no idea what that was trying to prove.
Auschwitz-Birkenau was the largest Nazi extermination and concentration camp, located in the Polish town of Oswiecim, 37 miles west of Cracow. One sixth of all Jews murdered by the Nazis were gassed at Auschwitz. In April 1940 SS chief Heinrich Himmler ordered the establishment of a new concentration camp in Oswiecim, a town located within the portion of Poland that was annexed to Germany at the beginning of World War II. The first Polish political prisoners arrived in Auschwitz in June 1940, and by March 1941 there were 10,900 prisoners, the majority of whom were Polish. Auschwitz soon became known as the most brutal of the Nazi concentration camps.
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]