<P> Hitler's reasons for declaring war against the US when he was not obligated to were numerous . One was an emotional response: the Japanese tactic of using a surprise attack without making a declaration of war appealed to him--he had done the same thing when he attacked the Soviet Union with Operation Barbarossa in June 1941; indeed, he told the Japanese ambassador "(O) ne should strike--as hard as possible--and not waste time declaring war ." Also, the prospect of a worldwide war fed Hitler's tendency towards grandiose thinking, and reinforced his feeling that he was a world - historical figure of destiny . As he said in his declaration speech to the Reichstag: </P> <P> I can only be grateful to Providence that it entrusted me with the leadership in this historic struggle which, for the next five hundred or a thousand years, will be described as decisive, not only for the history of Germany, but for the whole of Europe and indeed the whole world . </P> <P> Hitler's lack of knowledge about the US and its industrial and demographic capacity for mounting a war on two fronts also entered into his decision . As early as mid-March 1941--nine months before the Japanese attack--President Roosevelt was acutely aware of Hitler's hostility towards the United States, and the destructive potential it presented . Due to this attitude within the White House, and the rapidly progressing efforts of the Americans' industrial capacity before and through 1941 to start providing its armed forces with the ordnance, combat aircraft and ships that would be required to defeat the Axis as a whole, the US was already well on its way towards the full - scale wartime economy which would make it the "arsenal of democracy" for itself and its allies . </P> <P> Finally, Hitler's deeply - held racial prejudices made him see the US as a decadent bourgeois democracy filled with people of mixed race, a population heavily under the influence of Jews and "Negroes", with no history of authoritarian discipline to control and direct them, interested only in luxury and living the "good life" while dancing, drinking and enjoying "negrofied" music . Such a country, in Hitler's mind, would never be willing to make the economic and human sacrifices necessary to threaten National Socialist Germany--and thus set the stage for a dangerously inaccurate view of the very nation that Hitler had stated in his unpublished Zweites Buch (Second Book, 1928) would be the Third Reich's most serious challenge beyond his intended defeat of the Soviet Union . </P>

What caused the allies to declare war on germany