In A Nutshell:

This section is an overview of Japanese history, from the earliest times to the present. Unlike China and Korea, the borders of Japan have stayed relatively stable throughout most of its history due to its geographic status as a group of islands. Until the mid-20th century, historic Japan was never occupied by another people and in turn never held territorial possessions on the mainland or major islands nearby until the late 19th century– though attempts were made at colonizing the Korean peninsula in the late 16th century. From the late 19th century until 1945, the imperial Japanese government had colonies in Taiwan, Korea, northeast China and, during WWII, major parts of Southeast Asia. Since 1945, Japan has remained in its traditional territory, though a few islands are still held in dispute with various states in the region.