From 1910 to 1945, Korea was ruled as a part of the Empire of Japan under the Japanese name .
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 forcefully opened by the United States in the Perry Expedition. 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, it 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 the Korean 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. It began a process of Japanization, eventually functionally banning the use of Korean names and the Korean language altogether. It also created infrastructure and industry. Railroads, 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 country, and not to benefit its people. Many of the rural poor did not see the benefits of the infrastructure, and were required to send a significant amount of their agricultural output to Japan, which left many on the brink of ruin or starvation. 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. While the international consensus is that these incidents all occurred, various Japanese scholars and politicians, including Tokyo Governor Yuriko Koike, either deny completely, attempt to justify, or downplay incidents such as these. Beginning in 1939 and during World War II, Japan began conscripting hundreds of thousands of Koreans en masse 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. Some Japanese politicians and scholars, including now Prime Minister Fumio Kishida, deny that Koreans were forced laborers, and instead claim that they were "requisitioned against their will" to work. Women and girls aged 12–17 were infamously recruited, according to the international consensus, forcefully by Japan into functional sexual slavery. They are now euphemistically referred to as "comfort women", and are a continuing source of controversy. A number of modern Japanese scholars and politicians, notably from the far-right nationalist group Nippon Kaigi, of which Fumio Kishida and 57% of his cabinet are members of, deny that they were forced to work at all, and that even the pubescent girls consented to sex work and were compensated reasonably. After the surrender of Japan, Korea was liberated, although it was immediately divided under the rule of the Soviet Union and the United States.