Before the attack on Pearl Harbor had occurred, Japan and the United States had been allies but for the 10 years before the attack, the 2 nations had been having tense negotiations. However, when Japan started to go overboard with conquering land, the United States became angry. Japan was trying and conquering lands including Manchuria in 1931, and China in 1937. The United States were allies with China, and when they saw that Japan was taking over China, they were not too happy. So, they blocked transportation of goods that Japan needed; Japan was very angry with this so they blocked their transportation of goods to the United States. However, Japan wanted to do something more than just blocking goods, so they planned a surprise attack on America.