Why did the US supported China. why didn't the state's go to war sooner against japan?

The U.S. supported China primarily to counter Japanese aggression in East Asia and to promote stability in the region during the 1930s. This support included economic aid and military supplies, as the U.S. recognized the strategic importance of China in the fight against Japan. The U.S. did not go to war against Japan sooner due to a combination of isolationist sentiment, economic concerns, and a focus on domestic issues during the Great Depression. It wasn't until Japan's attack on Pearl Harbor in December 1941 that the U.S. was compelled to enter World War II.