Hitler was a mediocre man. A mediocre painter. A mediocre soldier.
(He would have made a great actor, but IMO the world of theater in the 1920s was too decadent and wild for this simple man.)
He returned from war and found his homeland Austria in political turmoil, caused by the Communists.
1. He started hating Communists.
2. Anti-Semitism had deep roots in european culture.
3. The racist misinterpretation of Darwinism was en vogue at that time.
The world was complicated and scary and he wanted to make it simple again.
He got dragged into politics when his talent for oratory became obvious.
And Hitler was never in it for money or fame: Eva Braun had to talk him into selling commemorative post-stamps with his face on them. He wasn't comfortable profiting financially from his political position.
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Mussolini was a troublemaker from early on. A visionary. A leader. A braggart.
While Hitler's politics were focused on the past, Mussolini's fascism was focused on the future.