Why did Hitler declare war on US in World War 2?

Answer 1

Germany declared war on the United States to honor its pact with Japan. Since Japan had actually attacked the United States, Germany did not actually have to declare war. Through the lend-lease program, the United States was also giving support to Great Britain, against whom Germany was at war; so the United States was definitely aiding a country that Germany was at war with.
It was in response to the US declaring war on Japan after the attacks on Pearl Harbor.
Germany & Italy declared war on the United States on December 11, 1941. This was four days after the Japanese began their surprise attacks to start war with the United States & the British Empire (Great Britain, Australia, New Zealand, Canada & South Africa).

On 27 September 1940 Japan joined Hitler & Mussolini in a military (cooperation) alliance called the 'Tripartite Pact', or the 'Axis' as it was called in Britain & US. However, Japan is not obligated to go to war with the current enemies of Germany and Italy. The three parties announce that they will declare war on any third party that attempts to enter the war against any one of the three. This is primarily aimed at the United States, to prevent America's entry into the war in Europe and prevent American interference in Asia. Although the Pact specifically excludes the USSR in its relations with Germany or Japan, Hitler's goal is to have Japan join in the war against Stalin when the time comes. Japan will successfully resist these urgings throughout the next five years.

By late 1941, Hitler was eager for war with the United States. This is because the United States (officially a neutral country) had become increasingly more friendly towards Britain and hostile towards Germany, during Hitler's war of aggression in Europe. By May 1940 it became clear to US President Roosevelt that Hitler's Germany was a dangerous threat to the United States, and that the US should do everything possible (short of war) to support Great Britain and her allies in their desperate struggle against Hitler. Most of the outward hostility centered around shipments of supplies & equipment to Great Britain from the United States & Canada across the North Atlantic Ocean. This situation was like a repeat of events during the First World War, where German U-Boats attacked all shipping in the Atlantic destined for the British Isles.

Hitler knew of his ally Japan's intentions to attack the US & Britain, but not when. When the Japanese attacks on the US & Britain were announced, Hitler rushed back to Berlin to prepare a Declaration of War against the US. His declaration also included a statement of solidarity with Japan & Italy and a 'no-separate peace' phrase. He wanted to make this declaration public before the US would declare war on Germany. However, President Roosevelt had no immediate intention of initiating the war against Germany, for practical moral & public relations reasons.

For Hitler's announced reasons for war, see below the actual text of the German announcement of its declaration of war, given to the US Charge d'Affairs in Berlin on December 11, 1941:

"The of the United States having violated in the most flagrant manner and in ever-increasing measure all rules of neutrality in favor of the adversaries of Germany and having continually been guilty of the most severe provocations toward Germany and since the outbreak of the European war, provoked by the British declaration of war against Germany on September 3, 1939, has finally resorted to open military acts of aggression.

On September 11, 1941, the President of the United States publicly declared that he had ordered the American Navy and Air Force to shoot on sight at any German war vessel. In his speech of October 27, 1941, he once more expressly affirmed that this order was in force. Acting under this order, vessels of the American Navy, since early September 1941, have systematically attacked German naval forces. Thus, American destroyers, as for instance the Greer, the Kearny and the Rueben James, have opened fire on German submarines according to plan. The Secretary of the American Navy, Mr. Knox, himself confirmed that American destroyers attacked German submarines.

Furthermore, the naval forces of the United States, under order of their Government and contrary to international law have treated and seized German merchant vessels on the high seas as enemy ships.

The German Government therefore establishes the following facts:

Although Germany on her part has strictly adhered to the rules of international law in her relations with the United States during every period of the present war, the Government of the United States from initial violations of neutrality has finally proceeded to open acts of war against Germany. The Government of the United States has thereby virtually created a state of war.

The German Government, consequently, discontinues diplomatic relations with the United States of America and declares that under these circumstances brought about by President Roosevelt, Germany too, as from today, considers herself as being in a state of war with the United States of America.

Accept, Mr. Charge d'Affairs, the expression of my high consideration."

The United States declared war on Germany & Italy on December 11, 1941, after they had declared war on the US.

Answer 2

The US had declared that a "state of war had existed" against Japan from the time they invaded Pearl Harbor. In a state of frenzy, Hitler using very poor judgment, invoked the war against the US because of the agreement with Japan and because of the assistance the US had been providing Great Britain.

This was a bad mistake on Hitler's behalf because there was every chance that the US would have withdrawn to fight off the Japanese without having to find reasons to devote time and effort to defeating Hitler. The declaration of war from Germany totally resolved the impasse.

This also illustrates the reason the British abandoned a plan to assassinate Hitler, his poor judgment and his systematic interference with the forces, was a great asset for the Allies.