I think be felt he had little to lose and everything to gain. The US was already at war with Germany by supplying the UK, just an undeclared one. If Hitler could unleash his U-Boats on the US and embargo the UK they'd have to sue for peace. With them gone the US would be hard pressed to fight Germany without a base of operations and might sue for peace too to focus on Japan.Hitler is often described as a "mad man" whose declaration of war against the U.S. was the worst strategic blunder of WW2. But I am wondering if there may have been a rational basis for his decision.
In December 1941 the German army was at the gates of Moscow, poised for what it seemed to be an imminent defeat of the USSR. In that event, Germany would have established an impregnable Fortress Europe for years to come. In contrast Germany's ally Japan was about to be squashed by the far greater industrial resources of the U.S., possibly creating a new world empire even more threatening to Germany than that of the British.
By quickly declaring war against the U.S. could Hitler have decided that drawing off U.S. resources to fight an unwinnable war in Europe would extend the war with Japan (possibly to a stalemate) and eventually lead to a comprehensive peace treaty?
There is almost no documentation of Hitler's thinking on this matter, but being a monster does not necessarily make one a moron. Any thoughts on this theory?