Look at maps of Europe and Asia before and after WWII, to understand ultimately what was accomplished by it on a geopolitical scope. That will help you understand why FDR was so desperate to get America involved and insure that the correct ideology prevailed.

While no one can excuse Japan’s belligerence in those days, it is also true that our government provoked that country in various ways — freezing her assets in America; closing the Panama Canal to her shipping; progressively halting vital exports to Japan until we finally joined Britain in an all-out embargo; sending a hostile note to the Japanese ambassador implying military threats if Tokyo did not alter its Pacific policies; and on November 26th — just 11 days before the Japanese attack — delivering an ultimatum that demanded, as prerequisites to resumed trade, that Japan withdraw all troops from China and Indochina, and in effect abrogate her Tripartite Treaty with Germany and Italy.

…The bait offered Japan was our Pacific Fleet. In 1940, Admiral J.O. Richardson, the fleet’s commander, flew to Washington to protest FDR’s decision to permanently base the fleet in Hawaii instead of its normal berthing on the U.S. West Coast. The admiral had sound reasons: Pearl Harbor was vulnerable to attack, being approachable from any direction; it could not be effectively rigged with nets and baffles to defend against torpedo planes; and in Hawaii it would be hard to supply and train crews for his undermanned vessels. Pearl Harbor also lacked adequate fuel supplies and dry docks, and keeping men far from their families would create morale problems. The argument became heated. Said Richardson: “I came away with the impression that, despite his spoken word, the President was fully determined to put the United States into the war if Great Britain could hold out until he was reelected.”