Japanese colonial empire; Wikimedia Commons.

In the early 20th Century, while mystical idealism, quest for world prestige and economics were important factors, Japan’s imperialism was principally a reaction against the encroachment of Western powers.

In the 1930s, in addition to the “independent” state of Manchukuo, Imperial Japan controlled Taiwan, Korea, Karafuto (Southern Sakhalin), the Kwantung Leased Territory and Nan’yō-chō (former German islands in Micronesia).

A good reference is The Japanese Colonial Empire:1895-1945 by RH Meyers and MR Peattie.