Korea (Korean: 한국, Hanguk or 조선, Joseon) is a peninsular region in East Asia. Since 1945, it has been divided at or near the 38th parallel, with North Korea (Democratic People's Republic of Korea) comprising its northern half and South Korea (Republic of Korea) comprising its southern half. Korea consists of the Korean Peninsula, Jeju Island, and several minor islands near the peninsula. The peninsula is bordered by China (Manchuria) to the north and Russia to the northeast, across the Amrok and Duman rivers. It is separated from Japan to the southeast by the Korea Strait.

During the first half of the 1st millennium, Korea was divided between three states, Goguryeo, Baekje, and Silla, together known as the Three Kingdoms of Korea. In the second half of the 1st millennium, Silla defeated and conquered Baekje and Goguryeo, leading to the "Unified Silla" period. Meanwhile, Balhae formed in the north, superseding former Goguryeo. Unified Silla eventually collapsed into three separate states due to civil war, ushering in the Later Three Kingdoms. Toward the end of the 1st millennium, Goguryeo was resurrected as Goryeo, which defeated the two other states and unified the Korean Peninsula as a single sovereign state. Around the same time, Balhae collapsed and its last crown prince fled south to Goryeo. Goryeo (also spelled as Koryŏ), whose name developed into the modern exonym "Korea", was a highly cultured state that created the world's first metal movable type in 1234. However, multiple incursions by the Mongol Empire during the 13th century greatly weakened the nation, which eventually agreed to become a vassal state after decades of fighting. Following military resistance under King Gongmin that ended Mongol political influence in Goryeo, severe political strife followed, and Goryeo eventually fell to a coup led by General Yi Seong-gye, who established Joseon on 17 July 1392. The first 200 years of the Joseon era were marked by relative peace, and during this time the Korean alphabet was created by Sejong the Great and Confucianism became increasingly influential in the kingdom.

Joseon's two centuries of peace were broken by foreign invasions and internal factional strife from 1592 to 1637. Most notable of these invasions is the Japanese invasions of Korea, which marked the end of the Joseon dynasty's early period. Several decades later, Joseon was invaded by the Jurchens and the Manchus in 1627 and 1636 respectively, leading to an increasingly harsh isolationist policy, for which the country became known as the "hermit kingdom" in Western literature. After the end of these invasions from Manchuria, Joseon experienced a nearly 200-year period of peace and prosperity, along with cultural and technological development. What power the kingdom recovered during its isolation waned as the 18th century came to a close. Faced with internal strife, power struggles, international pressure, and rebellions at home, the kingdom declined rapidly in the late 19th century.

During the later years of the dynasty, Korea's isolationist policy earned it the Western nickname of the "hermit kingdom". By the mid 19th century, with the country unwilling to modernize, and under encroachment of European powers, Joseon Korea was forced to sign unequal treaties with foreign powers. After the assassination of Empress Myeongseong in 1895, the Donghak Peasant Revolution, and the Gabo Reforms of 1894 to 1896, the Korean Empire (1897–1910) came into existence, heralding a brief but rapid period of social reform and modernization. However, in 1905, the Korean Empire signed a protectorate treaty and in 1910, Japan annexed the Korean Empire. Korea then became a Japanese colony from 1910 to 1945.

Japan relinquished control over Korea after formally surrendering to the Allies on 2 September 1945, in the aftermath of World War II. The Soviet Union and the United States had agreed to partition Korea along the 38th parallel, with the Soviets occupying the north and the Americans occupying the south. These circumstances became the basis for the division of Korea by the two superpowers with two different ideologies, exacerbated by their inability to agree on the terms of Korean independence. The communist government in the north received backing from the Soviet Union in opposition to the pro-Western government in the south, leading to Korea's division into two sovereign states in 1948: North Korea and South Korea. Tensions between the two resulted in North Korea invading South Korea and the outbreak of the Korean War in 1950. With involvement by foreign troops, the war ended in a stalemate in 1953, but without a formalised peace treaty. This status contributes to the high tensions that continue to divide the peninsula, and both states continue to claim to be the sole legitimate government of Korea. A breakthrough in the peace process came on 27 April 2018, when North Korea and South Korea signed the Panmunjom Declaration on ending the conflict and reunifying Korea.