One theory holds that Japan bombed Pearl Harbor to decimate the American Pacific fleet so Japan could spread its influence throughout the South Pacific. Another theory believes the bombing was intended to force the United States to accept an agreement to lift economic sanctions against Japan.
Japan and the United States saw their relationship sour throughout the late 1930s as Japan declared war and invaded China. Japan, which was going through economic and demographic problems, considered that invading China and spreading into the South Pacific would alleviate the problem. After the countries cut off diplomatic ties in 1941, war between the countries seemed a foregone conclusion, but the United States expected Japan to attack one of the relatively close European colonies in the South Pacific.