Pearl Harbor: declare war on the United States?

Adolf Hitler learns on 7 December of the Japanese attack on Pearl Harbor with barely concealed satisfaction. The Tripartite Pact of September 1940 binds Germany, Italy, and Japan in a defensive alliance: the mutual-assistance clause is triggered only when one of the signatories is attacked — yet it is Japan that struck first. Hitler is therefore under no legal obligation to act. For months he has kept his U-boats on a tight leash to avoid a fatal naval incident with Washington, well aware that American isolationist opinion remains the best bulwark against massive intervention in Europe. Franklin Roosevelt does not yet hold a war mandate against the Reich.

Yet the decision Hitler must make in the hours that follow will shape the entire course of the war. He can seize the momentum of Pearl Harbor and immediately declare war on the United States, cementing the alliance with Tokyo and finally unleashing the Kriegsmarine in the Atlantic. He can instead stay out of it, letting the Americans bog down in the Pacific while limiting himself to controlled naval incidents. Or he can play for time, deferring any formal declaration and negotiating behind the scenes the terms of solidarity with Japan.

Ribbentrop's pressure, pride and ideological logic push him toward the dramatic gesture. But the stakes go far beyond a show of solidarity: it means opening a second oceanic front against the foremost industrial power on earth.