Until December 11, 1941, the US and Nazi Germany were technically neutral despite World War II having ravaged large portions of Europe, the Middle East, and Asia.
But following Imperial Japan’s attack on Pearl Harbor and the beginning of hostilities between the US and the Axis Powers on December 7, 1941, Nazi Germany followed Japan’s lead and declared war on the US.
According to Rare Historical Photos, the decision to declare war was entirely Adolf Hitler’s. Even before Pearl Harbor, Hitler was aware that the US and Nazi Germany would eventually come to blows, since the US was supporting the British war effort.
The decision to enter the war was announced by Hitler at a speech at the Reichstag after the German and Italian embassies burned their cables in Washington, DC.