text: I'm assuming that this question is being asked from an American perspective as Britain and France declared war on Hitlers regime.\n\nIts actually a great question and very relevant to today.\n\nThe answer is that without Pearl Harbor and Germanys subsequent decision to stand alongside its Japanese allies and declare war on the U.S, it is likely that you would not have got involved in World War Two.\n\nAt that time the American public was very isolationist in its thinking and there was a huge politcal lobby against getting involved in another European war.\n\nBritish Prime Minister Winston Churchill devoted much of the time between 1939 and December 1941 trying to persuade Roosevelt to come to our aid militarily, but Roosvelt knew it would have been political suicide.\n\nMany americans were even against the supply of war materials to Britain when we were standing alone against the Germans who had conquered the rest of Europe.\n\nThese materiels, tanks planes, ships etc were vital to re-equip the British Army. \n\nThis wasnt a new thing either. The USA had kept out of World War 1 also until 1917 (the war started in 1914) for the same reasons. They only got involved then because of the sinking of a US ocean liner full of U.S civilians by a German submarine. \n\nIn both wars however the USA was the only power to emerge stronger economically, militarily and politically. \n\nIt is interesting to read these days however the comments by ordinary Americans again saying that the U.S should become isolationist again and leave the rest of the world to sort its own problems out.\n\nI hope that doesnt happen as the world needs a policeman, and the U.S is the only power big enough to do the job.