6 million is a rather large number. How did the allies come to this number?
Hi, just to be clear, the 6 million figure is a count of Jewish victims only - the capital-H Holocaust - not all victims. There was a post on Jewish victims and numbers the other day; check it out and click the link I provided there for a breakdown of the numbers
I have given a partial answer to this questions previously here. To quote from the response:
Newer scholarship estimates on the number of Jews killed in the Holocaust range somewhere in between 5.4 million people and 6.2 million people. This has to do with a problem in evidence. Despite the stereotype of the Nazis being super bureaucratic and writing everything down, they did in fact not keep an exact tally, especially where shootings and the extermination camps of Operation Reinhard as well as the non-Reinhard camp of Chelmno was concerned. Furthermore, the Nazis did indeed try to hide what they were doing, with which I deal here.
In order to arrive at the total figured, the methods historians' use is combining direct estimates, i.e. the number of victims in concentration camps, extermination camps, through killing squads plus all additional material about killed people, with methods of indirect statistical comparison, i.e. population statistics before and after the war. By combining the two methods and looking for a convergence of evidence on one range of figures versus another, we can estimate figures with a high degree of confidence. Given the lack of complete population statistics this number still has a margin of error (that's the reason for the range between 5.4 and 6.2 million) but not a margin of error so large that 6 million suddenly become 3 million or just hundred thousand.
Let me give you an example of how this works. A very important document in terms of establishing numbers is the so-called Korherr Report, which I have also linked. Richard Korherr was the head of the SS statistics bureau and in March 1943 he compiled a report about the decrease in Jewish population in Europe from 1932 to December 1942. He arrives at the conclusion that through normal decrease due to the death rate, due to emigration and due to German policy, the number of Jews in Europe has decreased about 4 million from 32 to 42. With regards to about 1.2 million Jews, he uses the phrase "Es wurden durchgeschleust durch die Lager im Generalgouvernement" (Guided through the camps in the General Government), which was what Himmler suggested he use instead of "Sonderbehandlung" (special treatment). This is Nazi code language for killed. So we know that by December 42, the head of the SS office for statistics gives a number of killed Jews that is 1.2 million.
However, several things need to be looked at in addition to the number Korherr gives here. First of all, the number of 1.2 million Korherr gives here seems to be correct in relation to the Operation Reinhard extermination camps. We can verify this number using the Höfle Telegram. The Höfle Telegram is an intercept from British intelligence. Sent originally on January 11, 1943 by Hermann Höfle, who was Odilo Globocnik's deputy in Operation Reinhard - the killing of the Jews of the General Government in the camps of Sobibor, Treblinka, and Belzec - it details the number of Jews that have arrived at the Operation Reinhard Camp by January 1943 and it also arrives at a total number of 1.2 million. So, using the Korherr Report with back up from the Höfle Telegram, we can assert with certainty that by January 1943, 1.2 million Jews had been killed in the Operation Reinhard Camps.
From the Korherr Report it is also possible to assert that Korherr did not have the Einsatzgruppen numbers. This comes from the Korherr Report itself where Korherr writes that he didn't count the Jews in Russia and on the frontline. The Einsatzgruppen reports are available to us. From June 1941 on, the Einsatzgruppen send detailed reports about their activities in the Soviet Union to Himmler and various other agencies. From those we can assert that by late 1941 the Einsatzgruppen killed at least 500.000 Jews in the Soviet Union. With the second round of killing that is less well documented, the total number of victims of the Einsatzgruppen by 43 comes through a variety of sources to about 1.5 million people. That combined with the numbers we have from Korherr shows that by mid-43 3 million Jews were already dead. And that does not account for the Jews killed in Auschwitz, the Jews killed in Poland during the operations in 1939, the Jews of Serbia being killed by the Wehrmacht and by gas van, the Aktion Harvest Festival in the Majdanek camp, the killing of the Hungarian Jews in 1944 and so on.
Combining all this evidence leads to numbers that have been compiled in this following table (courtesy of /u/elos_ and /u/searocksandtrees)
Country Est. Pre-War Jewish pop. Est. Jewish population killed Percent killed Poland 3,300,000 3,000,000 91 Baltic countries 253,000 228,000 90 Germany Camp; Austria 240,000 210,000 88 Bohemia Camp; Moravia 90,000 80,000 89 Slovakia 90,000 75,000 83 Greece 70,000 54,000 77 Netherlands 140,000 105,000 75 Hungary 650,000 450,000 70 Belorussian SSR 375,000 245,000 65 Ukrainian SSR 1,500,000 900,000 60 Belgium 65,000 40,000 60 Yugoslavia 43,000 26,000 60 Romania 600,000 300,000 50 Norway 1,800 900 50 France 350,000 90,000 26 Bulgaria 64,000 14,000 22 Italy 40,000 8,000 20 Luxembourg 5,000 1,000 20 Russian SFSR 975,000 107,000 11 Denmark 8,000 120 2 Finland 2,000 22 1 Total 8,861,800 5,933,922 67
So this should give you some insight into how historians today arrive at that number. The same process is applied to non-Jewish victims of the Nazis though in those cases it is a bit harder regarding Nazi documentation itself, which is why the total number of victims there ranges between 11 and 14 million people.
As for the Allies' estimation of Nazi victims, it was even higher in 1945, partly because as I mention in the linked answer, they assumed for example gas chambers always operating at full capacity, which was not the case, partly because people like Höss had boasted that they had killed more people than they actually did. Original estimated in 1945 ran between 8 and 10 million victims and were lowered after a the process I described above to the documents used in the IMT trials in Nuremberg. However, generally, Soviet estimates were always a big higher than those of Western scholarship.
On the Höfle Telegram: Peter Witte, Stephen Tyas: A New Document on the Deportation and Murder of Jews during „Einsatz Reinhard“ 1942. In: Holocaust and Genocide Studies 15, 2001, pp. 468–486.
On the Korherr Report: Gerald Fleming: Hitler und die Endlösung. Wiesbaden/München 1982.
On Auschwitz: Franciszek Piper: Die Zahl der Opfer von Auschwitz. Staatliches Museum Auschwitz, 1993.
Wolfgang Benz (Hrsg.): Dimensionen des Völkermords – Die Zahl der jüdischen Opfer des Nationalsozialismus., München 1996.
Raul Hilberg: The Destruction of the European Jews, Yale 2002.
Saul Friedlände: Nazi Germany and the Jews, Vol. 1 and 2.
Doris L. Bergen: War & Genocide: A Concise History of the Holocaust.
Christian Gerlach: The Extermination of the European Jews, 2016.
Nicholaus Wachsmann: KL. A history of the Nazi Concentration Camps, 2015.