Why did the united states place trade restrictions on japan before world war ii?

the United States, along with England and The U.S.S.R., was helping the Chinese.

japan had entered into war with the Chinese before war was declared in Europe.

Japan captured Manchuria and five other northern provices of China. The Japanesee ,wanted to stop all aid to China from the Allies and the United States. Thisrequest was turned down and the U.S. put an embargo on Japan. Japan was angered at this because they relied on the United States for many products that helped,their war effort, for example steel. Japan retaliated with the bombing of Pearl,Harbor on December 7, 1941. The Japanese attacked with six aircraft carriers.The U.S. lost eight battleships, three cruisers, four destroyers, five other ships, and 188 airplanes. U.S. casualties were 2,400 killed and 1,000 injured.