When exactly Hitler settled on straightforward murder as a means of removal has been harder to pinpoint. As Yale historian Timothy Snyder writes, “It cannot be stressed enough that the Nazis did not know how to eradicate the Jews when they began the war against the Soviet Union [in the summer of 1941]… They could not be confident that SS men would shoot women and children in large numbers.” But as Operation Barbarossa, the name for the Nazi invasion of the U.S.S.R, proved during the mass shootings of June 1941 and the massacres at Kiev in September, the Order Police and Einsatzgrüppen were more than willing to commit mass murders. This meant Hitler could take the solution to the Jewish problem to its “furthest extremes,” in the words of Philipp Bouhler, the senior Nazi official responsible for the euthanasia program that killed more than 70,000 handicapped German people.

Germany invaded the Soviet Union in June 1941.[236] German propaganda portrayed the war against the Soviet Union as both an ideological war between German National Socialism and Jewish Bolshevism and a racial war between the Germans and the Jewish, Romani and Slavic Untermenschen ("sub-humans").[237] Local populations in some occupied Soviet territories actively participated in the killing of Jews and others, and helped identify and round up Jews.[238] German involvement ranged from active instigation and involvement to general guidance.[239] In Lithuania, Latvia, and western Ukraine, locals were deeply involved in the murder of Jews from the beginning of the German occupation. Some of these Latvian and Lithuanian units also participated in the murder of Jews in Belarus. In the south, Ukrainians killed about 24,000 Jews and some went to Poland to serve as concentration and death-camp guards.[238] Military units from some countries allied to Germany also killed Jews. Romanian units were given orders to exterminate and wipe out Jews in areas they controlled.[240] Ustaše militia in Croatia persecuted and murdered Jews, among others.[168] Many of the killings were carried out in public, a change from previous practice.[241]

Another Polish courier, Jan Karski, reached the west in November 1942, carrying messages from Jewish leaders in Poland. He had himself witnessed the conditions in the Warsaw ghetto and in what he believed to be the Belzec death camp, and was eager to inform the world. Karski saw the British foreign secretary, Anthony Eden, and US President Roosevelt, but they seemed to be more interested in military intelligence than in atrocity stories. Partly as a result of Karski's mission, however, the Allies agreed to a joint declaration, read to the British Parliament on 17 December, which acknowledged Nazi war crimes and threatened punishment for the perpetrators. Subsequently millions of leaflets were dropped in the course of bombing raids on German cities to inform Germans of the facts, but these had little or no effect.

On January 20, 1942, Reinhard Heydrich convened the Wannsee Conference at a lakeside villa in Berlin to organize the “final solution to the Jewish question.” Around the table were 15 men representing government agencies necessary to implement so bold and sweeping a policy. The language of the meeting was clear, but the meeting notes were circumspect:
On June 6, 1944, also known as D-Day, more than 150,000 Allied soldiers landed in France. In December the Germans started an unsuccessful counterattack in Belgium and northern France, known as the Battle of the Bulge. Continuing to gain momentum, the Soviets began an offensive in January 1945, liberating western Poland and then forcing Hungary to surrender.
The Nazis then combined their racial theories with the evolutionary theories of Charles Darwin to justify their treatment of the Jews. The Germans, as the strongest and fittest, were destined to rule, while the weak and racially adulterated Jews were doomed to extinction. Hitler began to restrict the Jews with legislation and terror, which entailed burning books written by Jews, removing Jews from their professions and public schools, confiscating their businesses and property and excluding them from public events. The most infamous of the anti-Jewish legislation were the Nuremberg Laws, enacted on September 15, 1935. They formed the legal basis for the Jews' exclusion from German society and the progressively restrictive Jewish policies of the Germans.
Before the “Final Solution” was devised to murder all Jews in Nazi jurisdiction, the scheme the Nazis planned to rid their land of the Jews was forced emigration. In 1940, plans were devised by the Nazis to ship all Jews under Nazi control to Madagascar, an island in the Indian Ocean. It was not until 1941 that Nazi bureaucrats were referring to the “Final Solution” (Gesamtlosung) in the context of genocide rather than a “Territorial Final Solution” (territoriale Endlosung) in the context of forced emigration. Some historians believe that the Madagascar Plan was a smokescreen for Hitler’s desire to murder European Jewry (see page 62 of Marrus’ The Holocaust in History).

Trainloads of human cargo arriving at Auschwitz went through a selection process conducted by SS doctors such as Josef Mengele. Young adults considered fit for slave labor were allowed to live and had an ID number tattooed on their left forearm. Everyone else went to the gas chambers. A few inmates, including twin children, were occasionally set aside for participation in human medical experiments.

The roots of Hitler’s particularly virulent brand of anti-Semitism are unclear. Born in Austria in 1889, he served in the German army during World War I. Like many anti-Semites in Germany, he blamed the Jews for the country’s defeat in 1918. Soon after the war ended, Hitler joined the National German Workers’ Party, which became the National Socialist German Workers’ Party (NSDAP), known to English speakers as the Nazis. While imprisoned for treason for his role in the Beer Hall Putsch of 1923, Hitler wrote the memoir and propaganda tract “Mein Kampf”(My Struggle), in which he predicted a general European war that would result in “the extermination of the Jewish race in Germany.”

Genealogical Studies in the Cases of Cleft Lip-Jaw-Palate (1938), his medical dissertation, earned him a doctorate in medicine from Frankfurt University. Studying the influence of genetics as a factor in the occurrence of this deformity, Mengele conducted research on families who exhibited these traits in multiple generations. The work also included notes on other abnormalities found in these family lines.[7][122]
This was upgraded on 31 July 1941, when Hermann Goering sent an order that Heydrich should make “all necessary preparations with regard to organisational, practical and financial aspects for an overall solution to the Jewish question”. Heydrich was to “submit an overall plan… for the execution of the intended ‘Final Solution’ of the Jewish question”.
The Nazis established ghettos in occupied Poland. Polish and western European Jews were deported to these ghettos. During the German invasion of the Soviet Union in 1941, mobile killing squads (Einsatzgruppen) began killing entire Jewish communities. The methods used, mainly shooting or gas vans, were soon regarded as inefficient and as a psychological burden on the killers.
Uprisings broke out in some extermination camps. The few remaining Jews kept alive to dispose of bodies and sort possessions realised the number of transportees was reducing and they would be next. Civilian uprisings occurred across Poland as mainly young Jews, whose families had already been murdered, began to resist Nazi oppression. With reports of rebellion and mass murder in the British press, the situation in the camps could no longer be be ignored.

Peter Longerich argues that the search for a finite date on which the Nazis embarked upon the extermination of the Jews is futile, in his book Holocaust: The Nazi Persecution and Murder of the Jews (2011). Longerich writes: "We should abandon the notion that it is historically meaningful to try to filter the wealth of available historical material and pick out a single decision" that led to the Holocaust.[116][117]
Several resistance groups were formed, such as the Jewish Combat Organization in the Warsaw Ghetto and the United Partisan Organization in Vilna.[310] Over 100 revolts and uprisings occurred in at least 19 ghettos and elsewhere in Eastern Europe. The best known is the Warsaw Ghetto Uprising of 1943, when around 1,000 poorly armed Jewish fighters held the SS at bay for four weeks.[311][q] During a revolt in Treblinka on 2 August 1943, inmates killed five or six guards and set fire to camp buildings; several managed to escape.[316][317] In the Białystok Ghetto on 16 August 1943, Jewish insurgents fought for five days when the Germans announced mass deportations.[318] On 14 October 1943, Jewish prisoners in Sobibór, including Jewish-Soviet prisoners of war, attempted an escape,[319] killing 11 SS officers and a couple of Ukrainian camp guards.[320] Around 300 escaped, but 100 were recaptured and shot.[321] On 7 October 1944, 300 Jewish members of the Sonderkommando at Auschwitz, who learned they were about to be killed, attacked their guards and blew up crematorium IV. Three SS officers were killed, one of whom was stuffed into an oven, as was a German kapo. None of the Sonderkommando rebels survived the uprising.[322]
Similarly, in Ordinary Men (1992), Christopher Browning examined the deeds of German Reserve Police Battalion 101 of the Ordnungspolizei ("order police"), used to commit massacres and round-ups of Jews, as well as mass deportations to the death camps. The members of the battalion were middle-aged men of working-class background from Hamburg, who were too old for regular military duty. They were given no special training. During the murder of 1,500 Jews from Józefów in Poland, their commander allowed them to opt out of direct participation. Fewer than 12 men out of a battalion of 500 did so. Influenced by the Milgram experiment on obedience, Browning argued that the men killed out of peer pressure, not bloodlust.[471]
On 6 January 1942, the Soviet Minister of Foreign Affairs, Vyacheslav Molotov, sent out diplomatic notes about German atrocities. The notes were based on reports about bodies surfacing from poorly covered graves in pits and quarries, as well as mass graves found in areas the Red Army had liberated, and on witness reports from German-occupied areas.[335] The following month, Szlama Ber Winer escaped from the Chełmno concentration camp in Poland, and passed detailed information about it to the Oneg Shabbat group in the Warsaw Ghetto. His report, known by his pseudonym as the Grojanowski Report, had reached London by June 1942.[288][336] Also in 1942, Jan Karski sent information to the Allies after being smuggled into the Warsaw Ghetto twice.[337][s] On 27 April 1942, Vyacheslav Molotov sent out another note about atrocities.[335] In late July or early August 1942, Polish leaders learned about the mass killings taking place inside Auschwitz. The Polish Interior Ministry prepared a report, Sprawozdanie 6/42,[340] which said at the end:
So the following year, in June 2016, Freund returned with two groups of researchers and their equipment and for the first time mapped the unknown areas of the site, including any unmarked mass graves. Then, using a collection of aerial photographs of Ponar shot by Nazi reconnaissance planes and captured during the war, which helped give the researchers a better sense of the camp’s layout, Freund and his colleagues turned their attention to finding clues about how the camp’s fabled survivors were able to find a way out. (A “Nova” television documentary about the discoveries found in Vilnius, "Holocaust Escape Tunnel" will premiere on PBS on April 19. Check your local listings for times.)
The murder industry began in the Chelmno camp, built in December 1941. Work was carried out in special trucks, where the victims were asphyxiated by exhaust fumes, a method that had been tried before on those whose lives were deemed useless (the “Euthanasia Pro­gram”). From September 1939, about 100,000 “Aryan” Germans were assassinated in this manner, in what was named “Operation T4.” Two years later, the personnel responsible for the “euthanasia” program were called upon to apply their expertise to murdering Jews. In the single camp of Chelmno, 150,000 human beings were gassed to death, most of them brought to the camp from annexed territories, the Warthegau district of western Poland and the Lodz Ghetto.
The Roma refer to the genocide of the Romani people as the Pořajmos.[414] Because they are traditionally a private people with a culture based on oral history, less is known about their experience than that of any other group.[415] Bauer writes that this can be attributed to the Roma's distrust and suspicion, and to their humiliation because some of the taboos in Romani culture regarding hygiene and sex were violated at Auschwitz.[416] In May 1942, the Roma were placed under similar laws to the Jews. On 16 December 1942, Himmler issued a decree that "Gypsy Mischlinge [mixed breeds], Roma Gypsies, and members of the clans of Balkan origins who are not of German blood" should be sent to Auschwitz, unless they had served in the Wehrmacht.[417] He adjusted the order on 15 November 1943; in the occupied Soviet areas, "sedentary Gypsies and part-Gypsies are to be treated as citizens of the country. Nomadic Gypsies and part-Gypsies are to be placed on the same level as Jews and placed in concentration camps."[418] Bauer argues that this adjustment reflected Nazi ideology that the Roma, originally an Aryan population, had been "spoiled" by non-Romani blood.[419]
After obtaining a copy of his birth certificate through the West German embassy in 1956, Mengele was issued with an Argentine foreign residence permit under his real name. He used this document to obtain a West German passport, also using his real name, and embarked on a trip to Europe.[71][72] He met up with his son Rolf (who was told Mengele was his "Uncle Fritz")[73] and his widowed sister-in-law Martha, for a ski holiday in Switzerland; he also spent a week in his home town of Günzburg.[74][75] When he returned to Argentina in September 1956, Mengele began living under his real name. Martha and her son Karl Heinz followed about a month later, and the three began living together. Josef and Martha were married in 1958 while on holiday in Uruguay, and they bought a house in Buenos Aires.[71][76] Mengele's business interests now included part ownership of Fadro Farm, a pharmaceutical company.[74] Along with several other doctors, Mengele was questioned in 1958 on suspicion of practicing medicine without a license when a teenage girl died after an abortion, but he was released without charge. Aware that the publicity would lead to his Nazi background and wartime activities being discovered, he took an extended business trip to Paraguay and was granted citizenship there in 1959 under the name "José Mengele".[77] He returned to Buenos Aires several times to settle his business affairs and visit his family. Martha and Karl lived in a boarding house in the city until December 1960, when they returned to Germany.[78]