The Japanese military had a strong hold on the government and sought to ensure economic security through colonialism. The saw that the western powers had claimed good territories and sought out to claim territories of their own. They tried to claim China in the 1930s which ended with the people turning on the Japanese.
The Americans had power over oil resources and refused to supply oil to the Japenese and the froze assets in the US. The Japenese military retaliated by attacking the Americans hence the attack on Pearl Harbour. This started World War 2.
