They irrigated dry lands. hope it helps
Arkansas, Missouri, Iowa, Oklahoma, Kansas and Nebraska. I am pretty sure those are them. Sorry if i'm wrong
In 1922, the U.S.-driven Washington Naval Conference resulted in the Nine-Power Treaty reaffirming the Open Door principles. In reaction to the Mukden Incident of 1931 in Manchuria and the Second Sino-Japanese War between China and Japan in 1937, the United States intensified its support of the Open Door Policy.