His biggest mistake was declaring war on the United States. His belief that he was allying with a country that had never been defeated in war (Japan) was utterly staggering. The second was invading Russia in 1941. He went a year too early. Imagine diverting some of those resources to clearing the Med. The North African theater would have been a completely different affair with even 2 or 3 extra divisions and 1 extra luftflotte to safeguard the supply routes.
For all that, thank god he made those mistakes
