During the late 19th century Japan emerged as an increasingly militarist power backed by an expanding population and industrial base. Japan became an ally of Britain, remaining so when Britain entered World War I. As a result of the Allied victory in 1918 Japan was awarded the German colonial possessions across the central Pacific. Throughout the 1930s Japan became increasingly a expansionist. Following a Chinese attack on the Japanese-owned Manchurian Railway, in 1931 the Japanese Kwangtung Army invaded Manchuria, setting up a puppet government, without the permission of the government in Tokyo. The military now became the dominant element in the governance of Japan and her empire, and in 1937 the Kwangtung army invaded the Republic of China. Japan had developed the theory of the Great East Asia Co-Prosperity Sphere, which placed the people and industry of Japan at its core. With the colonial powers in the region at war or occupied by the Axis powers of Germany and Italy, to which Japan had allied itself, only the United States with its Pacific possessions stood in the way. The Japanese plan was to strike the US navy at its base at Pearl Harbor with maximum force, whilst seizing a wide, defensible perimeter containing the resources necessary to maintain a war with the United States. The strike on Pearl Harbor went ahead on 7 December 1941 and the Pacific War began.
— OR —