How did Korea become a Japanese colony, and why is its legacy still disputed?

Through a series of steps that took only five years, each backed by force or pressure. Japan's victory over Russia in 1905 removed its main rival, and in the Treaty of Portsmouth Russia acknowledged Japan's paramount political, military and economic interest in Korea. Korea became a Japanese protectorate that same year, and in 1910 Japan formally annexed it. From 1910 to 1945 Korea was a colony under the name Chōsen.

The protectorate treaty came with "reforms" that cut the Korean army from 20,000 men to 1,000. In 1907 Emperor Gojong was forced to abdicate. Resistance did not stop. In 1909 a Korean nationalist, Ahn Jung-geun, assassinated Ito Hirobumi, a former Japanese prime minister, in Harbin.

Life under colonial rule was shaped by a basic contradiction. Koreans were nominally granted Japanese citizenship, but they were denied basic rights such as freedom of speech, assembly and an independent press. Railways, ports and roads were built, and one account says economic output grew tenfold between 1910 and 1945, yet scholars argue that many projects were designed to extract resources rather than to benefit Koreans.

In March 1919, about two million people are estimated to have joined peaceful protests across Korea. Japan suppressed them violently. Korean records count 7,509 people killed, Japanese figures 553.

The period is still contested. Historians hold a wide range of opinions about it in both South Korea and Japan, and historical topics from it regularly cause diplomatic issues between the two countries.