America wanted Japan to stop attempting to take over China and Indonesia,because the US did not want them to expand their empire. Japan was given an ultimatum, either stop trying to take over countries, or the Allies would stop giving them raw materials. Japan chose to stop receiving raw materials from the Allies. Because of America,The Netherlands and The UK freezing and reducing the materials they gave them, this angered Japan, and Japan's anger was a key reason behind the bombing of Pearl Harbor and why Japan decided to it. .
Despite China's rejection and their resources being reduced,by the end of 1941 however, Japan had taken over French Indochina, formerly a french colonised region, in Southeast Asia. Japan's army was now at 2,400,000 well-trained ground troops, and 7,500 airplanes while America merely had 1,500,000 troops, a majority of which had not completed training yet. Although Japan failed to have more warships than America. US Navy commanders Lieutenant/General Walter Short and Admiral were first sent a warning on October 16th, 1941 about Japan's intentions to Pearl Harbor. The US Army in Washington did not agree with the warning and did not believe Japan was going to attack the United States. .
The main reason Japan attacked Pearl Harbor was because they believed that it was "their only threat and needed to be destroyed". .
The attack on Pearl Harbor was organised by Isoroku Yamamoto, who was a Japanese Marshal Admiral in the Japanese Imperial Navy. Isoroku Yamamoto was also was the commander in chief for the Combined Fleet, a temporary organisation that was created by the Japanese Imperial Navy to help them with their defenses in case of a threat. Isoroku Yamamoto won the approval from high commanders in the imperial navy,by saying he'd resign if they did not agree to this plan. Isoroku Yamamoto, began planning the attack in early 1941. He eventually won the approval of Japan's Emperor Hirohito Showa and a date in December 1941 was planned for the attack.