Japan remained closed to most of the outside world until the middle of the 19th century. Trade incursions from Europe and the United States forced Japan to establish its role in the international community, and the country emerged as an aggressive imperial power. Japan's efforts to acquire territory increased rapidly at the close of the 19th century, and eventually resulted in official colonies in five areas.

Korea

Japan initiated its control over Korea with an 1876 treaty that established Korea as a so-called “protected state.” A 1905 treaty transitioned Korea into an official Japanese protectorate, while the Japan-Korea Annexation Treaty of 1910 established Korea as a full-fledged colony. Japan maintained its control of Korea until the end of World War II. While Japan ruled harshly, especially for the first decade, colonialism also brought many modern improvements to Korea. For example, at the end of World War II, Korea was second only to Japan itself in terms of industrial development among Asian countries.

Taiwan

The current Republic of China has distinction as Japan’s first official overseas colony. Japan’s efforts to take control of Taiwan, which date to at least the 16th century, met fruition in 1895, after Japan defeated China in the First Sino-Japanese War. China ceded control of Taiwan in perpetuity, and Japan began to develop its new possession as a model colony to showcase its power. As a result, even after Taiwan regained independence at the end of World War II, Chinese in Taiwan tend to have more favorable opinions of Japan than mainland Chinese.

Sakhalin

Sakhalin, a Russian island north of Japan, inspired disputes between the two countries beginning in the early 19th century. Beginning in the 1840s, Russians settled the island in defiance of Japan’s claim of sovereignty. Japan ceded the southern part of Sakhalin in 1875, but regained control in 1905 as a term of victory in the Russo-Japanese War. The southern half of Sakhalin, known as the Karafuto Prefecture, remained under Japanese control until the end of World War II.

South Pacific Mandate

Japan’s efforts against Germany in World War I resulted in the Treaty of Versailles' recognition of Japanese sovereignty over former German possessions in the South Pacific. The South Pacific Mandate consisted of several groups of islands, including Micronesia, Palau, and the Northern Mariana and Marshall Islands. Japan put these islands to extensive strategic use in World War II and officially relinquished control in 1947.

Regions of Mainland China

Japan’s repressive occupation of the current People’s Republic of China has served as a source of antipathy between the two nations ever since. Manchuria, an area in northeast China, became the site of some of Japan’s worst imperial atrocities. Japan acquired Kwantung, an area in southern Manchuria, in the aftermath of the Russo-Japanese War. In 1928, Japan assassinated Manchuria’s leader and installed a puppet government, which persisted until a Soviet invasion in 1945. Shandong Province, a center of Chinese culture, became a Japanese colony under the Treaty of Versailles. Japan relinquished control in 1922, but occupied the province again in 1937.