Korea under Japanese rule

From 1910 to 1945, Korea was ruled by the Empire of Japan under the name Chōsen (朝鮮), the Japanese reading of "Joseon".

Japan first took Korea into its sphere of influence during the late 1800s. Both Korea (Joseon) and Japan had been under policies of isolationism, with Joseon being a tributary state of Qing China. However, in 1854, Japan was forcibly opened by the United States. It then rapidly modernized under the Meiji Restoration, while Joseon continued to resist foreign attempts to open it up. Japan eventually succeeded in opening Joseon with the unequal Japan–Korea Treaty of 1876.

Afterwards, Japan embarked on a decades-long process of defeating its local rivals, securing alliances with Western powers, and asserting its influence in Korea. Japan assassinated the defiant Korean queen and intervened in the Donghak Peasant Revolution. After Japan defeated China in the 1894–1895 First Sino–Japanese War, Joseon became nominally independent and declared the short-lived Korean Empire. Japan then defeated Russia in the 1904–1905 Russo-Japanese War, making it the sole regional power. It then moved quickly to fully absorb Korea. It first made Korea a protectorate with the Japan–Korea Treaty of 1905, and then ruled the country indirectly through the Japanese resident-general of Korea. After forcing Emperor Gojong to abdicate in 1907, Japan then formally colonized Korea with the Japan–Korea Treaty of 1910. The territory was then administered by the governor-general of Chōsen, based in Keijō (Seoul), until the end of the colonial period.

Japan made sweeping changes in Korea. Under the pretext of the racial theory known as Nissen dōsoron, it began a process of Japanization, eventually functionally banning the use of Korean names and the Korean language altogether. Tens of thousands of cultural artifacts were taken to Japan, and hundreds of historic buildings like the Gyeongbokgung and Deoksugung palaces were either partially or completely demolished. Japan also built infrastructure and industry. Railways, ports, and roads were constructed, although in numerous cases workers were subjected to extremely poor working circumstances and discriminatory pay. While Korea's economy grew under Japan, many argue that many of the infrastructure projects were designed to extract resources from the peninsula, and not to benefit its people. Most of Korea's infrastructure built during this time was destroyed during the 1950–1953 Korean War.

These conditions led to the birth of the Korean independence movement, which acted both politically and militantly sometimes within the Japanese Empire, but mostly from outside of it. Koreans were also subjected to a number of mass murders, including the Gando Massacre, Kantō Massacre, Jeamni massacre, and Shinano River incident.

Beginning in 1939 and during World War II, Japan mobilized around 5.4 million Koreans to support its war effort. Many were moved forcefully from their homes, and set to work in generally extremely poor working conditions, although there was a range in what people experienced. Women and girls were controversially forced into sexual slavery as "comfort women". After the surrender of Japan at the end of the war, Korea was liberated, although it was immediately divided under the rule of the Soviet Union and of the United States.

The legacy of Japanese colonization was hotly contested even just after its end, and is still extremely controversial. There is a significant range of opinions in both South Korea and Japan, and historical topics regularly cause diplomatic issues. Within South Korea, a particular focus is the role of the numerous ethnic Korean collaborators with Japan, who have been variously punished or left alone. This controversy is exemplified in the legacy of Park Chung Hee, South Korea's most influential and controversial president, who collaborated with the Japanese military and continued to praise it even after the colonial period. Until 1964, South Korea and Japan had no functional diplomatic relations, until they signed the Treaty on Basic Relations, which declared "already null and void" the past unequal treaties, especially those of 1905 and 1910. Despite this, relations between Japan and South Korea have oscillated between warmer and colder periods, often due to conflicts over the historiography of this era.