Hwaseong Fortress, a UNESCO World Heritage Site, in 2019 In 936, the Later Three Kingdoms were united by Wang Geon, who established Goryeo as the successor state of Goguryeo.[14][15][75][76] Balhae had fallen to the Khitan Empire in 926, and a decade later the last crown prince of Balhae fled south to Goryeo, where he was warmly welcomed and included in the ruling family by Wang Geon, thus unifying the two successor nations of Goguryeo.[77] Like Silla, Goryeo was a highly cultural state, and invented the metal movable type printing press.[26] After defeating the Khitan Empire, which was the most powerful empire of its time,[78][79] in the Goryeo–Khitan War, Goryeo experienced a golden age that lasted a century, during which the Tripitaka Koreana was completed and significant developments in printing and publishing occurred. This promoted education and the dispersion of knowledge on philosophy, literature, religion, and science. By 1100, there were 12 universities that produced notable scholars.[80][81] However, the Mongol invasions in the 13th century greatly weakened the kingdom. Goryeo was never conquered by the Mongols, but exhausted after three decades of fighting, the Korean court sent its crown prince to the Yuan capital to swear allegiance to Kublai Khan, who accepted and married one of his daughters to the Korean crown prince.[82] Henceforth, Goryeo continued to rule Korea, though as a tributary ally to the Mongols for the next 86 years. During this period, the two nations became intertwined as all subsequent Korean kings married Mongol princesses,[82] and the last empress of the Yuan dynasty was a Korean princess. In the mid-14th century, Goryeo drove out the Mongols to regain its northern territories, briefly conquered Liaoyang, and defeated invasions by the Red Turbans. However, in 1392, General Yi Seong-gye, who had been ordered to attack China, turned his army around and staged a coup. Yi Seong-gye declared the new name of Korea as "Joseon" in reference to Gojoseon, and moved the capital to Hanseong (one of the old names of Seoul).[83] The first 200 years of the Joseon dynasty were marked by peace and saw great advancements in science[84][85] and education,[86] as well as the creation of Hangul by Sejong the Great to promote literacy among the common people.[87] The prevailing ideology of the time was Neo-Confucianism, which was epitomized by the seonbi class: nobles who passed up positions of wealth and power to lead lives of study and integrity. Between 1592 and 1598, Japan under Toyotomi Hideyoshi launched invasions of Korea, but the advance was halted by Korean forces (most notably the Joseon Navy led by Admiral Yi Sun-sin and his renowned "turtle ship") with assistance from righteous army militias formed by Korean civilians, and Ming dynasty Chinese troops.[88] Through a series of successful battles of attrition, the Japanese forces were eventually forced to withdraw, and relations between all parties became normalized. However, the Manchus took advantage of Joseon's war-weakened state and invaded in 1627 and 1637 and then went on to conquer the destabilized Ming dynasty. After normalizing relations with the new Qing dynasty, Joseon experienced a nearly 200-year period of peace. Kings Yeongjo and Jeongjo particularly led a new renaissance of the Joseon dynasty during the 18th century.[89][90] In the 19th century, Joseon began experiencing economic difficulties and widespread uprisings, including the Donghak Peasant Revolution. The royal in-law families had gained control of the government, leading to mass corruption and weakening of the state.[citation needed] In addition, the strict isolationism of the Joseon government that earned it "the hermit kingdom" became increasing ineffective due to increasing encroachment from powers such as Japan, Russia, and the United States. This is exemplified by the Joseon–United States Treaty of 1882, in which it was compelled to open its borders. Japanese occupation and World War II Main article: Korea under Japanese rule In the late 19th century, Japan became a significant regional power after winning the First Sino-Japanese War against Qing China and the Russo-Japanese War against the Russian Empire. In 1897, King Gojong, the last king of Korea, proclaimed Joseon as the Korean Empire. However, Japan compelled Korea to become its protectorate in 1905 and formally annexed it in 1910. What followed was a period of forced assimilation, in which Korean language, culture, and history were suppressed.[91] This led to the March First Movement protests in 1919 and the subsequent foundation of resistance groups in exile, primarily in China. Among the resistance groups was Provisional Government of the Republic of Korea.[92] Towards the end of World War II, the U.S. proposed dividing the Korean peninsula into two occupation zones: a U.S. zone and a Soviet zone. Dean Rusk and Charles H. Bonesteel III suggested the 38th parallel as the dividing line, as it placed Seoul under U.S. control. To the surprise of Rusk and Bonesteel, the Soviets accepted their proposal and agreed to divide Korea.[93] Division of Korea Ceremony for the inauguration of the South Korean government (August 15, 1948) Despite intentions to liberate a unified peninsula in the 1943 Cairo Declaration, escalating tensions between the Soviet Union and the United States led to the division of Korea into two political entities in 1948: North Korea and South Korea. In the South, the United States appointed and supported the former head of the Korean Provisional Government Syngman Rhee as leader. Rhee won the first presidential elections of the newly declared Republic of Korea in May 1948. In the North, the Soviets backed a former anti-Japanese guerrilla and communist activist, Kim Il Sung, who was appointed premier of the Democratic People's Republic of Korea in September.[94] In October, the Soviet Union declared Kim Il Sung's government as sovereign over both the north and south. The UN declared Rhee's government as "a lawful government having effective control and jurisdiction over that part of Korea where the UN Temporary Commission on Korea was able to observe and consult" and the government "based on elections which was observed by the Temporary Commission" in addition to a statement that "this is the only such government in Korea."[95] Both leaders engaged in authoritarian repression of political opponents.[96] South Korea requested military support from the United States but was denied,[97] and North Korea's military was heavily reinforced by the Soviet Union.[98][99] Korean War On June 25, 1950, North Korea invaded South Korea, sparking the Korean War, the Cold War's first major conflict, which continued until 1953. At the time, the Soviet Union had boycotted the UN, thus forfeiting their veto rights. This allowed the UN to intervene in a civil war when it became apparent that the superior North Korean forces would unify the entire country. The Soviet Union and China backed North Korea, with the later participation of millions of Chinese troops. After an ebb and flow that saw both sides facing defeat with massive losses among Korean civilians in both the north and the south, the war eventually reached a stalemate. During the war, Rhee's party promoted the One-People Principle, an effort to build an obedient citizenry through ethnic homogeneity and authoritarian appeals to nationalism.[100] The 1953 armistice, never signed by South Korea, split the peninsula along the demilitarized zone near the original demarcation line. No peace treaty was ever signed, resulting in the two countries remaining technically at war. Approximately 3 million people died in the Korean War, with a higher proportional civilian death toll than World War II or the Vietnam War, making it one of the deadliest conflicts of the Cold War era.[101][102] In addition, virtually all of Korea's major cities were destroyed by the war.[103] Miracle on the Han River Main a