"The occasion for this piece is a seemingly straightforward question: why did Adolf Hitler and the Nazi regime so quickly declare war on the United States just four days after Imperial Japan’s attack on Pearl Harbor? There is nothing self-evident about this. Moscow had not fallen to the Wehrmacht during Operation Typhoon, Britain was still very much in the war, and resistance against German rule had burgeoned from France to Greece. The late Fritz Stern characterized Hitler’s rush to support Japan on December 11, 1941 against the United States as “a move historians still find puzzling.”