Why did Hitler believe in German superiority?

Answer Why do tall people think tall is better? Why do brown eyed people think brown eyes are better? Hitler was attempting to appeal to the people of his nation in his attempt to take over Europe. He told them what they wanted to hear, and they loved it as is evidenced by the fact that they let him get away with mass murder. They were, as a group, narcissistic, with the firm conviction that they were, in fact, superior to the rest of us. They truly believed that they were undefeatable. Unfortunately for them, they only proved to be inflexible. Hitler was making them obey his instructions, and forcing them to follow it. --- The key thing was not the belief in superiority but the actions that it was used to justify.

The above is certainly the the case for the hardened Nazi, but as was evidenced by the two plots against his life, one of which was hatched before September 1, 1939, not all Germans believed as Hitler did.

Once Hitler had taken full power in 1934 ( in 1933 he was head of the government as Chancellor, and when he became President in 1934 he was also head of the State ) by fear and action he had a strong hold over Germany. All German opposition was eliminated, and even fellow Nazis who disagreed with him were also killed.

Fear is a strong element for the forces of the evil Hitler represented.