Evidence of the existence of the Holocaust was well documented by the heavily bureaucratic German government itself. It was further well documented by the Allied forces who entered Germany and its associated Axis states towards the end of World War II. Among the evidence produced was film and stills of the existence of prisoner camps, as well as the testimony of those freed when the camps were entered.
The Holocaust was a massive undertaking that lasted for years across several countries, with its own command and control infrastructure. Although the Nazis made attempts to destroy the evidence of the Holocaust when they could see that their defeat was imminent, they left many tons of documents relating to the Holocaust. Due to the extremely rapid collapse of the Nazi forces at the end of the war, attempts to destroy evidence in Germany were for the most part unsuccessful.
After their defeat, many tons of documents were recovered, and many thousands of bodies were found not yet completely decomposed, in mass graves near many concentration camps. The physical evidence and the documentary proof included records of train shipments of Jews to the camps, orders for tons of cyanide and other poisons, and the remaining concentration camp structures. Interviews with survivors completed the picture.
As a result of the records produced, all mainstream historians agree that Holocaust denial is contrary to the facts of history.
Deniers consider one of their stronger arguments to be the population of Jews before and after the Holocaust. They claim that the 1940 World Almanac gives the world Jewish population as 15,319,359, while the 1949 World Almanac gives the world Jewish population as 15,713,638. In their view this makes it impossible that 6 million Jews died, even given an extremely high birth rate. They therefore claim that either the figures are wrong, or the Holocaust, meaning the deliberate extermination of millions of Jews, cannot have happened.
However, as is typically the case, the evidence given by Holocaust deniers does not stand up to closer scrutiny. In fact, the 1949 World Almanac gives the world Jewish population as 11,266,600. Moreover, it revises its estimate of the World Jewish population in 1939 upwards, to 16,643,120. Thus, according to the 1949 World Almanac the difference between the pre and post war populations is over 5.4 million.
In addition, rather than using more accurate census figures and other records, Holocaust deniers rely on a popular compendium whose methodology of assessment is unknown, and whose estimates have varied significantly. For example, the 1982 World Almanac gives the world Jewish population as 14,318,000, while the 1990 World Almanac gives the world Jewish population as 18,169,000, and the 1996 World Almanac gives the world Jewish population as 13,451,000. Either 3.7 million Jews appeared unnoticed between 1982 and 1990, and then 4.5 million Jews disappeared equally unnoticed between 1990 and 1996, or the World Almanac is not a particularly reliable source for accurate estimates of worldwide Jewish population.
Finally, Holocaust deniers can be very selective when citing sources; other sources give very different figures for the Jewish population before and after the war. For example, the 1932 American Jewish yearbook estimate the total number of Jews in the world at 15,192,218, of whom 9,418,248 resided in Europe. However, the 1947 yearbook states: "Estimates of the world Jewish population have been assembled by the American Jewish Joint Distribution Committee (except for the United States and Canada) and are probably the most authentic available at the present time. The figures reveal that the total Jewish population of the world has decreased by one-third from about 16,600,000 in 1939 to about 11,000,000 in 1946 as the result of the annihilation by the Nazis of more than five and a half million European Jews. In Europe only an estimated 3,642,000 remain of the total Jewish pre-war population of approximately 9,740,000."
This selectivity means that Holocaust deniers often ignore the documents produced by the Nazis themselves, who used figures of between 9 and 11 million for the Jewish population of Europe, as evidenced in the notes of the Wannsee Conference. In fact, the Nazis methodically recorded the ongoing reduction of the Jewish population, as in the Korherr Report, which gave the status of the Final Solution through December, 1942:
The total number of Jews in the world in 1937 is generally estimated at around 17 million, thereof more than 10 million in Europe... From 1937 to the beginning of 1943 the number of Jews, partially due to the excess mortality of the Jews in Central and Western Europe, partially due to the evacuations especially in the more strongly populated Eastern Territories which are here counted as off-going, should have diminished by an estimated 4 million. It must not be overlooked in this respect that of the deaths of Soviet Russian Jews in the occupied Eastern territories only a part was recorded, whereas deaths in the rest of European Russia and at the front are not included at all.... On the whole European Jewry should since 1933, i.e. in the first decade of National Socialist German power, have lost almost half of its population.