World War II had campaigns occurring in Asia and the Pacific Ocean.
Empire of Japan . Economic and political turmoil in the 1920s led to the rise of militarism , eventually culminating in Japan 's membership in the Axis alliance and the conquest of a large part of the Asia-Pacific region . World War II . In December 1941 , Japan attacked the United States and European colonies in the Pacific Ocean , and quickly conquered much of the Western Pacific .