On this day in 1941, Adolf Hitler declared war on the United States. The question that historians (at least American historians) always ask is why. It is true that Hitler was not really required to do so. The German-Italian-Japanese Tripartite Pact that was signed in September 1940 was a defensive alliance, and the war that came between Japan and the United States on December 7, 1941 most assuredly was a result of offensive action by Japan. In fact, knowing that the Tripartite Pact did not require Germany to go to war, both Churchill and Roosevelt were extremely concerned that Hitler would not declare war. Both regarded Germany as a much more pernicious threat to the world than Japan, and both knew that the American public would not support an American declaration of war against Germany after Pearl Harbor. Roosevelt desperately wanted the US involved in the European war, and Hitler bailed him out. Hitler's decision is usually presented as an unaccountable blunder that virtually assured German defeat in the war. It was undeniably a blunder, but, as Ian Kershaw points out in his new book Fateful Choices: Ten Decisions That Changed the World, 1940-1941, it wasn't exactly an unaccountable one.
Kershaw argues that one must remember the context of Hitler's decision. By early December 1941, the German attack on the Soviet Union had bogged down, and it was clear that Hitler's gamble that he could crush the Soviets in 1941 had lost. The Soviets began their counteroffensive, which came very close to breaking the German army, on December 5. Hitler was desperate to get the Japanese into the war, against the Soviets ideally but against the British if need be. Furthermore, while the United States and Germany were not technically at war before Hitler made his declaration, they almost might as well have been. In fact, the United States had been waging undeclared war in the north Atlantic since fall. The Kreigsmarine had been begging Hitler to allow them to begin unrestricted submarine warfare (indeed, just to fire back when US Navy ships tried to sink them) for months. He had held them off, but it was clear that he couldn't forever. So, put yourself in Hitler's position. Declaring war binds Japan more closely to the Axis and may eventually induce them to go to war with the Soviet Union, at a time when the war with the Soviet Union isn't exactly going well. What's more, Germany is already at war with the US in all but name. What difference does it make to make it official? That's likely what Hitler was thinking, and it has a certain logic to it. It doesn't change the fact that it was a blunder, but the blunder was understandable.