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Hitler hated Jews mainly because that's how he was brought up, anti-semitism was rampant during his childhood in Austria, with many politicians planning to deport the Jewish population to Palestine. There was a lot of anti Semitic litature hanging around blaming Jews for economic troubles and stereotyping them as caring about nothing but money.
Hitler firmly believed that Jews were the cause of the German loss in ww1, that they influenced the treaty Versailles that destroyed the German economy, and that the Jews were not only communists, but the root of communism. Communist leaders had started taking control of Germany near the end of war around 1918, he believed that their economic policies weakened Germany making them incapable of continuing the war.
Adolf was in a lot of ways a product of his time, there are no single events that you can point to that explains his anti Semitic views, but instead it was his entire upbringing, his society, and those he associated with.0