WWII started when Hitler tried to expand Germany and eradicate anyone who wasn't a pure Aryan, yes, but Hitler first served as a soldier in WWI. WWI started when the Arch-duke of Austria-Hungary was assassinated, about which they thought Serbia was involved. Since Austria-Hungary and Germany were allies, they both decided to declare war. After failing art school, before WWI, Hitler was a homeless bum that sold his art in the streets. When WWI started, Hitler enlisted as a soldier. Hitler was taken prisoner by the enemy and released after the war. When he found out his country had surrendered, he felt humiliated. He joined a legal secret service, investigating fascist regimes until he found out he liked fascism. He joined the party and became the head of it. He decided to overthrow the government. He was arrested for organizing a riot but was released early. During his 9 months in prison, he wrote a book.
Also, Hitler wasn't German.