Why hadn't America joined the war before pearl harbour?

Answer 1

When the Japanese seized Manchuria and then invaded China and began to drive to the south they put their country on the road to war with the United States. The aggression was a result of the West's efforts to weaken Japan as an economic rival after WW1. The Great depression, Japan's population explosion and the need to find new resources/markets to continue as a first rate power were other causes of the invasion. Neither Japan nor America would have come to the brink of war except for the social and economic disruption of Europe after WW1 and the rise of communism and fascism. FDR brought the differences to a head on the night of July 26, 1941 after learning that the Japanese army had pushed into Indochina and he froze all Japanese assets in America. This resulted in all trade with Japan was stopped and Amercia the major source of oil imports for Japan left them in a bad positions. On November 20 Washington promised bit ti make any more aggressive moves south, restore peace in China and remove all troops in southern Indochina to the north of that country. In return America was to sell Japan a million tons of aviation gasoline.

Bitter political controversy had clouded the issue of war or peace in America. Interventionist were convinced that the nation's future depended on its helping crush the aggression of other nations. They pushed through the Lend Lease Act committing America to unlimited aid "short of war." to the enemies of the Axis. The United States would be the "arsenal of democracy". The opponents of intervention were the right wing American Firsters of Charles Lindbergh, Senator Borah, the communist and labor parties, and the isolationist Midwest. Pearl Harbor decided the question.

Answer 2

Because we had just finished with WWI and didn't want to fight in another war. The US called it isolationalism and didn't plan to until Japan bombed Pearl Harbor on December 7, 1941.

Answer 3

Isolationism.

The US was war weary from the first world war, and saw the outbreak of a second one as a European matter that did not concern them.