Korea, called Hanguk (Korean: 한국; Hanja: 韓國) in South Korea and Joseon (Korean: 조선; Hanja: 朝鮮) in North Korea, is an East Asian territory that is divided into two distinct sovereign states, North Korea (a.k.a. Democratic People's Republic of Korea, or DPRK) and South Korea (a.k.a. Republic of Korea, or ROK). Located on the Korean Peninsula, Korea is bordered by China to the northwest and Russia to the northeast. It is separated from Japan to the east by the Korea Strait and the East Sea . The adoption of the Chinese writing system ("Hanja" Korean: 한자 in Korean) in the 2nd century BC and the introduction of Buddhism in the 4th century AD had profound effects on the Three Kingdoms of Korea, which were first united during Silla (57 BC – AD 935) under King Munmu. The united Silla fell to Goryeo in 935 at the end of the Later Three Kingdoms period. Goryeo was a highly cultured state and created the Jikji in the 14th century. The invasions by the Mongolians in the 13th century, however, greatly weakened the nation, which was forced to become a tributary state. After the Mongol Empire's collapse, severe political strife followed. The Ming-allied Joseon emerged supreme in 1388.The first 200 years of Joseon were marked by relative peace and saw the creation of the Korean Hangul alphabet by King Sejong the Great in the 14th century and the increasing influence of Confucianism. During the later part of the dynasty, however, Korea's isolationist policy earned it the Western nickname of the "Hermit kingdom". By the late 19th century, the country became the object of the colonial designs by Japan. In 1910, Korea was annexed by Japan and remained a colony until the end of World War II in August 1945.In 1945, the Soviet Union and the United States agreed on the surrender of Japanese forces in Korea in the aftermath of World War II, leaving Korea partitioned along the 38th parallel, with the north under Soviet occupation and the south under U.S. occupation. These circumstances soon became the basis for the division of Korea by the two superpowers, exacerbated by their inability to agree on the terms of Korean independence. The two Cold War rivals then established governments centered on their own respective ideologies, leading to Korea's division into two political entities: North Korea and South Korea.