Quote from The Holocaust: An Introductory History, Jewish Virtual Library:
The Holocaust (also called Ha-Shoah in Hebrew) refers to the period from January 30, 1933 - when Adolf Hitler became chancellor of Germany - to May 8, 1945, when the war in Europe officially ended. During this time, Jews in Europe were subjected to progressively harsher persecution that ultimately led to the murder of 6,000,000 Jews (1.5 million of these being children) and the destruction of 5,000 Jewish communities. These deaths represented two-thirds of European Jewry and one-third of all world Jewry.
The Jews who died were not casualties of the fighting that ravaged Europe during World War II. Rather, they were the victims of Germany's deliberate and systematic attempt to annihilate the entire Jewish population of Europe, a plan Hitler called the “Final Solution” (Endlosung).
( http://www.jewishvirtuallibrary.org/jsource/Holocaust/history.html )
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