Based on the experiments with gas vans and temporary gas chambers at Auschwitz, SS leaders concluded that stationary killing centers would be the most efficient and (for the killers) psychologically viable form of mass murder. Thus, as of early 1942, the Nazis embarked on the most notorious project of the Holocaust: the creation of the extermination camps. Extermination camps were not the same thing as concentration camps. Concentration camps were prison camps, some of which created during the first weeks of Nazi rule in 1933. There were literally tens of thousands of concentration camps of various kinds scattered across the entire breadth of German-controlled territory. Extermination camps, however, were designed for one purpose: to kill people. There were only six of them in total, and most were very small - often about a quarter of a square mile in size. All were located in occupied Poland, near rail lines and hidden in forests away from major population centers. They were not meant to house prisoners for slave labor; new arrivals to an extermination camp were typically dead within two hours. They were, in short, "death factories," production facilities of murder that ran on industrial timetables.
The height of the Holocaust was thus shockingly short. It lasted from early 1942, when the extermination facilities were put into operation, until the late summer of 1943, a period of just over a year that saw 50% of the Jewish victims of the Holocaust itself murdered. The major reason for that incredible speed is that the ghettos of Poland were emptied into the extermination camps. The extermination camp Treblinka alone killed at least 800,000 people, most of whom were sent from the enormous ghetto of Warsaw. The millions of Jews who had been in Poland and the Russian territories of the west were murdered at a stunning, completely unprecedented rate.
The most infamous of the camps is unquestionably Auschwitz. Auschwitz was a great exception among the extermination camps in that it did house Jewish prisoners who were not immediately killed. Instead, about 80% of new arrivals to Auschwitz were sent immediately to their deaths in the gas chambers, while the other 20% were used temporarily for slave labor. More is known about day-to-day life inside of a death camp from Auschwitz because a relatively large number of its victims survived the war, although "relative" in this case still means "far less than 1%." Likewise, the infamous tattoos issued to prisoners were only performed at Auschwitz; there was no point in tattooing victims who were to be killed within hours, after all.
Within Auschwitz, not just Jews but regular criminals, enemies of the Nazi regime, Romani, and various other groups were housed in grossly overcrowded barracks. These prisoners were treated differently by German and auxiliary guards based on who they were and where they from, and they were actively encouraged to treat each other differently based on those distinctions as well. Non-Jewish German criminals were given important positions as kapos, team leaders, who oversaw Jewish slaves in the construction of new buildings in the vast, sprawling Auschwitz camp complex (it was over 20 kilometers across, including numerous sub-camps) or working in factories designed to support the German war effort. Of the approximately 200,000 Jews who were spared immediate murder on arrival, the large majority were either worked to death or murdered in the gas chambers after becoming too weak to work.
The five death camps besides Auschwitz operated from early 1942 until the fall or winter of 1943. They were used primarily to murder the Jews of Poland and their total death toll was approximately 1.5 million victims. In turn, they were never meant to be permanent: there were no large-scale slave labor facilities and only a handful of Jews were kept alive on arrival to work as slaves for the guards and to burn the bodies of their fellow victims after they were gassed (the survival rate from the three major camps besides Auschwitz was one one-thousandth of 1%, or .0001 to 1, representing the 150 people who survived and the 1.5 million who did not). Slave revolts occurred at two camps in August and October of 1943, which explains the fact that anyone survived these camps, but by then the camps had already succeeded: almost the entire Polish Jewish population was dead, starved in the ghettos or gassed in the camps. Afterwards, the SS destroyed the remains of the camps to hide the evidence of what had happened there.
Auschwitz, however, had been built to be permanent. Its gas chambers were large and made of concrete and steel (unlike the wood sheds used to murder in the other extermination camps). It was intended to be the final destination for every Jew captured by the Nazis in the years to come, and thus most Jews from the western European countries occupied by Germany were sent to die in Auschwitz. The Nazis continued to prioritize the "final solution" even as the war turned against them, shipping hundreds of thousands to Auschwitz as the Allies steadily pressed against them in the east and south.
One of the most bizarre and chilling episodes of the Holocaust was the Nazi takeover of Hungary in mid-1944. There, in what had been a staunch German ally, over 700,000 Jews had survived the war, “protected” in the sense that the Hungarian government had resisted the demands of the Germans to turn over its Jews for murder. When the Germans learned that the Hungarians were negotiating with the Soviets to switch allegiances, now that the German defeat was all but assured by early 1944, they supported a coup by Hungarian fascists under the direction of the Nazi state. That summer, at an astonishing rate, SS specialists overseeing Hungarian fascist police deported over 500,000 Hungarian Jews to Auschwitz. The vast majority were killed on arrival; in the Fall of 1944 Auschwitz was operated at its maximum capacity of killing up to 12,000 people a day. It bears emphasizing that the Holocaust was regarded by the top Nazi leadership as being a priority that was at least as high as actually fighting the war. Even after the war was evidently lost, tremendous efforts were made to kill every Jew then in German hands.
In early 1945, as the Soviet army closed from the east and the western Allies from the west, the Nazis initiated a series of death marches from the camps in Poland. Jewish prisoners that had survived up to that point, against incredible odds, were forced to march up to twenty miles through the Polish winter, then loaded into cattle cars and shipped into Germany. The western Allies - mostly Britain and the US - discovered the first evidence of the Holocaust when they liberated these German camps, discovering tens of thousands of corpses and thousands of horribly malnourished survivors. Likewise, the Soviet army liberated Auschwitz itself, discovering the gas chambers and the smattering of survivors who had been left behind when the Germans fled. Ultimately, the Holocaust ended because the war ended. The Nazis had been intent on "winning the Holocaust" even after it was self-evident that they could not win the war.