The bombing of Pearl Harbor surprised even Germany. Although Hitler had made an oral agreement with his Axis partner Japan that Germany would join a war against the United States, he was uncertain as to how the war would be engaged. Japan’s attack on Pearl Harbor answered that question. On December 8, Japanese Ambassador Oshima went to German Foreign Minister von Ribbentrop to nail the Germans down on a formal declaration of war against America. Von Ribbentrop stalled for time; he knew that Germany was under no obligation to do this under the terms of the Tripartite Pact, which promised help if Japan was attacked, but not if Japan was the aggressor. Von Ribbentrop feared that the addition of another antagonist, the United States, would overwhelm the German war effort. Hitler thought otherwise. He was convinced that the United States would soon beat him to the punch and declare war on Germany. The U.S. Navy was already attacking German U-boats, and Hitler despised Roosevelt for his repeated verbal attacks against his Nazi ideology. He also believed that Japan was much stronger than it was, that once it had defeated the United States, it would turn and help Germany defeat Russia. So at 3:30 p.m. (Berlin time) on December 11, the German charge d’affaires in Washington handed American Secretary of State Cordell Hull a copy of the declaration of war.
In easier words, Hitler thought the USA was going to start war first, and Hitler was already angry with the U-Boats attacks. So on December 11th, 1941, Hitler declared war.
