Korea under the Joseon dynasty had traditionally been invaded by multiple Manchurian and Japanese armies in its history. After the 1630's, though, Manchuria gave up on trying to conquer Korea, instead focusing on China. As Japan had no interest in restarting their invasions either, Korea welcomed an almost 200 year peace.
However, Korea would not keep foreign influence away forever. Nicknamed "the hermit kingdom" due to its self induced isolation, Korea was eventually forced to open its borders to trade. The Japanese, as imperialistic as the westerners, saw Korea as an opportunity. In the 1870s, Japan began to force Korea out of Manchuria's traditional sphere of influence and into its own. As a result of the Sino-Japanese War (1897-1910) the Manchurian Qing Dynasty was forced to accept Japan's advances without comment. In that same year, Empress Myeongseong was assassinated by Japanese agents.
The Empire of Korea had, until this time, entered a period of modernization of the military, the economy, and the justice system. However, with the Russian Empire being removed from the position of influencing Korea after the disastrous Russo-Japanese War of 1904, Japan was the only imperialist power left with interests in Korea. In 1910, the Japanese invaded. A treaty of annexation was circulated, and was signed by Lee Wang-Yong, who had been given the General Power of the Attorney by the Emperor. There is some debate as to whether or not the Emperor actually signed the treaty, as the Japanese never released the document. Though the treaty was internationally illegal, being signed under duress, due to threat of force and through bribery, the international community turned a blind eye.
The Japanese soon proved tyrannical masters. Millions of Koreans were used as forced labourers by the Japanese, and during wartime a large number of conscripted Koreans swelled the Japanese ranks. Korean culture came under threat, with Japanese attempts to eradicate the Korean Language and numerous Korean cultural artifacts destroyed or sent to Japanese museums. Koreans where forced to take Japanese names, a policy known as Soshi-kaimei. As with the rest of the sphere, Japan encouraged its citizens to immigrate to its new colonies. Japanese in Korea soon occupied the majority of the upper class.
These injustices where not o. The Korean Liberation Front, working in conjunction with rebels in Japanese Siberia and Manchukuo, attempted to drive the Japanese out of Korea. At first, protests where peaceful, but the Japanese soon reacted with force. 7000 demonstrators where killed by Japanese military and police forces on May 1st, 1919, during a demonstration. After this, resistance continued, with attacks being carried out of Japanese officials and attempts to sabotage Japanese works. However, the resistance was ill-coordinated and suffered chronic infiltration by collaborators.
In 1950, after the Great East Asian War, Japan lost a large amount of its manpower, not to mention a significant part of its economy. The Sphere was given increased independence, although the Japanese ensured that they controlled the economies of all member nations.
In 1951, Japan declared Korea to be an independent republic, hoping to appease the more moderate Koreans. However, it was not a true democracy, as the Japanese used a campaign of propaganda, bribery and assassination to ensure that politicians against Japan's intentions did not hold office. The Korean Revolutionary Party, formed of the Korean Liberation Front, sought to undermine Japanese influence, but too often fell victim to these tactics.
The economy improved in the following years, as with the rest of the Sphere. Japan continued to be necessary to the nation's survival, but to a lesser extent then before. Support for Japan among the Koreans, once non-existent, began to grow, in no small part due to the Japanese policy of propaganda.
On May 1st 1999, the Korean Liberation front, along with members of the Korean Revolutionary Party and numerous other politicians, using arms supplied by China, rose against the Korean government in a coup, declaring the Korean Republic was no longer a part of the Sphere. The uprising was initially very successful, with local police forces either defecting or being overwhelmed by the rebels. Japan was sluggish to respond, with the current generation of military inexperienced to warfare. Japan's generals ordered Japanese troops to intervene, in concert with the Korean Loyalists. The Korean Rebels held most of Western Korea in 2002, with the Japanese holding the eastern half of the country. The rebels endured due to support from China and the Philippines, although the rest of the South Asian Union was reluctant to intervene.
The Korean resistance started to crumble when on New Years Day, 2003, GEACPS satellites unleashed Kinetic Strike weaponry on Separatist positions. Although space based lasers had been used in combat to intercept missiles and destroy bunkers for a decade, and spy satellites had been used for at least 25 years, this action was completely unexpected by the Korean rebels. After the main cities and fortifications of the Koreans where hit, the Japanese had proven their ability to strike anywhere. The Separatists were forced by this to resort to their emergency contingency plan, guerrilla warfare. However, the GEACPS forces have used their superior numbers and supplies to weaken the Korean resistance. As of 2010, few pockets of resistance remain.