Uniquely at Auschwitz, prisoners were tattooed with a serial number, on their left breast for Soviet prisoners of war[97] and on the left arm for civilians.[98] Categories of prisoner were distinguishable by triangular pieces of cloth (German: Winkel) sewn onto on their jackets below their prisoner number. Political prisoners (Schutzhäftlinge or Sch), mostly Poles, had a red triangle, while criminals (Berufsverbrecher or BV) were mostly German and wore green. Asocial prisoners (Asoziale or Aso), which included vagrants, prostitutes and the Roma, wore black. Purple was for Jehovah's Witnesses (Internationale Bibelforscher-Vereinigung or IBV)'s and pink for gay men, who were mostly German.[99] An estimated 5,000–15,000 gay men prosecuted under German Penal Code Section 175 (proscribing sexual acts between men) were detained in concentration camps, of which an unknown number were sent to Auschwitz.[100] Jews wore a yellow badge, the shape of the Star of David, overlaid by a second triangle if they also belonged to a second category. The nationality of the inmate was indicated by a letter stitched onto the cloth. A racial hierarchy existed, with German prisoners at the top. Next were non-Jewish prisoners from other countries. Jewish prisoners were at the bottom.[101]
When three refugee physicists confided to Einstein that the Nazis might be developing a new weapon—an atomic bomb—he decided to act. Despite his previous appeals for governments to dispense with the weapons of war, Einstein wrote to President Franklin Roosevelt in 1939 alerting him to "a new phenomenon that would...lead to the construction of bombs" and suggested that the United States accelerate its atomic weapons research program. Scholars debate the effect of this letter. Einstein signed it in 1939 and the Manhattan Project, the U.S. effort to build the bomb, began in 1941.
Auschwitz I, a former Polish army barracks, was the main camp (Stammlager) and administrative headquarters of the camp complex. Intending to use it to house political prisoners, Reichsführer-SS Heinrich Himmler, head of the Schutzstaffel (SS), approved the site in April 1940 on the recommendation of SS-Obersturmbannführer (lieutenant colonel) Rudolf Höss, then of the Concentration Camps Inspectorate. Höss oversaw the development of the camp and served as its first commandant, with SS-Obersturmführer (senior lieutenant) Josef Kramer as his deputy.[21] Around 1,000 m long and 400 m wide,[22] Auschwitz I consisted of 20 brick buildings, six of them two-story; a second story was added to the others in 1943 and eight new blocks were built.[23] The camp housed the SS barracks and by 1943 held 30,000 inmates.[22] The first 30 prisoners arrived on 20 May 1940 after being transported from the Sachsenhausen concentration camp in Oranienburg, Germany. Convicted German criminals (Berufsverbrecher), the men were known as "greens" after the green triangles they were required to wear on their prison clothing. Brought to the camp as functionaries, this group did much to establish the sadism of early camp life, which was directed particularly at Polish inmates, until the political prisoners began to take over their roles.[4]

Umbreit, Hans (2003). "Hitler's Europe: The German Sphere of Power". In Kroener, Bernhard; Müller, Rolf-Dieter; Umbreit, Hans. Germany and the Second World War, Vol. 5. Organization and Mobilization in the German Sphere of Power. Part 2: Wartime Administration, Economy, and Manpower Resources, 1942–1944/5. Oxford; New York: Oxford University Press. ISBN 978-0-19-820873-0.
The racialists were not capable of drawing the practical conclusions from correct theoretical judgements, especially in the Jewish Question. In this way, the German racialist movement developed a similar pattern to that of the 1880s and 1890s. As in those days, its leadership gradually fell into the hands of highly honourable, but fantastically naïve men of learning, professors, district counsellors, schoolmasters, and lawyers—in short a bourgeois, idealistic, and refined class. It lacked the warm breath of the nation's youthful vigour.[175]
I have already said I that our barracks were overcrowded. It should be added that, although these barracks contained toilets and washrooms, neither came up to the most modest demands of modern hygiene. The cleansing of our bodies took place in a special room and was limited to a short washing of the upper extremities with cold water. A weekly warm shower was supposed to be provided, but with the overcrowding of the camp it was several weeks before a bath was available for each one. There was, of course, no toilet paper.
By 1944 over a half million women served as auxiliaries in the German armed forces.[284] The number of women in paid employment only increased by 271,000 (1.8 percent) from 1939 to 1944.[285] As the production of consumer goods had been cut back, women left those industries for employment in the war economy. They also took jobs formerly held by men, especially on farms and in family-owned shops.[286]

After 1942, many small subcamps were set up near factories to provide forced labor. IG Farben established a synthetic rubber plant in 1942 at Monowitz concentration camp (Auschwitz III); other camps were set up next to airplane factories, coal mines and rocket propellant plants. Conditions were brutal and prisoners were often sent to the gas chambers or killed on site if they did not work quickly enough.

From a contemporary U.S. perspective, however, the most interesting area of influence that Whitman explores is in immigration law. From the outset, the United States had a racially restricted immigration regime. The Naturalization Act of 1790, passed by the First Congress, limited immigration to “free white person[s].” In the 1800s, the United States passed more racially exclusionary immigration laws because of the perceived threat of Asians. As Whitman notes, the Nazis “almost never mentioned the American treatment of blacks without also mentioning the American treatment of other groups, in particular Asians and Native-Americans.” The Chinese were excluded from citizenship in the late 1800s, and the Asiatic Barred Zone of 1917 expressly banned immigration from a whole swath of Asia. Finally, the Immigration Act of 1924 set racial quotas for those who could enter the United States, and banned Indians, Japanese, Chinese, and other Asians outright, along with nearly all Arabs. Under the Cable Act of 1922, if a woman married an Asian man, her U.S. citizenship would be revoked. There were similar race-based immigration laws in Canada, Australia, New Zealand, and South Africa. Discrimination against immigrants on the basis of race was the norm, and in the United States it survived until the Immigration and Nationality Act of 1965, which is also the principal legislation that today’s white nationalists seek to undo. The Nazis had much to envy, what with the porous borders of Europe and the humiliating foreign treaties that had crippled Germany.

However, after the Nazis' "Seizure of Power" in 1933, Röhm and the Brown Shirts were not content for the party to simply carry the reigns of power. Instead, they pressed for a continuation of the "National Socialist revolution" to bring about sweeping social changes, which Hitler, primarily for tactical reasons, was not willing to do at that time. He was instead focused on rebuilding the military and reorienting the economy to provide the rearmament necessary for invasion of the countries to the east of Germany, especially Poland and Russia, to get the Lebensraum ("living space") he believed was necessary to the survival of the Aryan race. For this, he needed the co-operation of not only the military, but also the vital organs of capitalism, the banks and big businesses, which he would be unlikely to get if Germany's social and economic structure was being radically overhauled. Röhm's public proclamation that the SA would not allow the "German Revolution" to be halted or undermined caused Hitler to announce that "The revolution is not a permanent condition." The unwillingness of Röhm and the SA to cease their agitation for a "Second Revolution", and the unwarranted fear of a "Röhm putsch" to accomplish it, were factors behind Hitler's purging of the SA leadership in the Night of the Long Knives in July 1934.[281][282]
In general, subcamps that produced or processed agricultural goods were administratively subordinate to Auschwitz-Birkenau. Subcamps whose prisoners were deployed at industrial and armaments production or in extractive industries (e.g., coal mining, quarry work) were administratively subordinate to Auschwitz-Monowitz. This division of administrative responsibility was formalized after November 1943.
Use of the word "concentration" came from the idea of confining people in one place because they belong to a group that is considered undesirable in some way. The term itself originated in 1897 when the "reconcentration camps" were set up in Cuba by General Valeriano Weyler. In the past, the U.S. government had used concentration camps against Native Americans and the British had also used them during the Second Boer War. Between 1904 and 1908, the Schutztruppe of the Imperial German Army operated concentration camps in German South-West Africa (now Namibia) as part of its genocide of the Herero and Namaqua peoples. The Shark Island Concentration Camp in Lüderitz was the largest camp and the one with the harshest conditions.