The Holocaust was the systematic mass murder of approximately 6 million European Jews and millions of others by the Nazi regime during World War 2. Hitler blamed the Jews for Germany's loss in WWI and economic troubles, and outlined a plan for their elimination in his book Mein Kampf. When he rose to power, the Nazis passed laws stripping Jews of rights and isolating them, which culminated in mass killings in death camps and the murder of 2/3 of Europe's Jewish population. Roma, Slavs, Jehovah's Witnesses, homosexuals and others were also imprisoned and murdered in the Holocaust.