Hitler wrote the following in Mein Kampf:
Every manifestation of human culture, every product of art, science, and technical skill, which we see before our eyes today, is almost exclusively the product of the Aryan creative power. This very fact fully justifies the conclusion that it was the Aryan alone who founded a superior type of humanity; therefore he represents the archetype of what we understand by the term: MAN.
Picking up on virulent racist ideology of the late nineteenth century, Hitler targeted the Jews as the "disease" in the "blood" of the "volk" (Aryan Germans). He perceived the Jews as undermining Germany's strength and power. He saw history in terms of racial struggle, in which the strongest races survived and the weak were subjugated. He looked with approval on US policy towards the Native Americans, and the Turkish genocide of the Armenians. He believed it imperative for world history that the Aryan race survive and thrive; otherwise, as he said in Mein Kampf, the world would plunge into a new dark ages.
Hitler was not alone in his anti-semitism, which was widespread at the time and led countries like England and the United States to limit the number of Jewish refugees they would take.
Hitler blamed a Jewish so-called backstab for Germany's defeat in World War I. He conflated Judaism and communism, which he loathed, and he thought Jews would impose communism on Germany if they had a chance. He decided (historians debate exactly when) that his only option was to eradicate all the Jews. The difference between his anti-semitism and that of the rest of the West was that he went far beyond discrimination and the occasional violent pogrom and actually attempted genocide.
The Jews also provided a convenient scapegoat for a political demagogue whose power was based on stirring up hate. The in-group needs an out-group to despise. Jews comprised less than one percent of the German population, and so were a convenient target to a demagogue and a bully.