Korea is a region in East Asia. Since 1948 it has been divided between two distinct sovereign states, North Korea and South Korea. Korea consists of the Korean Peninsula, Jeju Island, and several minor islands near the peninsula. Korea is bordered by Russia to the northeast, China to the northwest, and neighbours Japan to the east via the Korea Strait and the Sea of Japan (East Sea).
During the first half of the 1st millennium, Korea was divided between the three competing states of 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 which 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 in July 17, 1392.
The first 200 years of the Joseon era were marked by relative peace. During this period, the Korean alphabet was created by Sejong the Great in the 15th century and there was increasing influence of Confucianism. During the later part of the dynasty, Korea's isolationist policy earned it the Western nickname of the "Hermit Kingdom". By the late 19th century, the country became the object of imperial design by the Empire of Japan. After the First Sino-Japanese War, despite the Korean Empire's effort to modernize, the country was annexed by Japan in 1910 and ruled by it 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. The North was 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 Communist-inspired 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 political entities: North Korea (officially the Democratic People's Republic of Korea), and South Korea (officially the Republic of Korea). Tensions between the two resulted in the outbreak of the Korean War in 1950. With involvement by foreign troops, the war ended in a stalemate in 1953, but without a formalized peace treaty. This status contributes to the high tensions that continue to divide the peninsula. Both governments of the two Koreas claim to be the sole legitimate government of the region.
"Korea" is the modern spelling of "Corea", a name attested in English as early as 1614. Korea was transliterated as Cauli in The Travels of Marco Polo, of the Chinese 高麗 (MC Kawlej, mod. Gāolì). This was the Hanja for the Korean kingdom of Goryeo (Korean: 고려; Hanja: 高麗; MR: Koryŏ), which ruled most of the Korean peninsula during Marco Polo's time. Korea's introduction to the West resulted from trade and contact with merchants from Arabic lands, with some records dating back as far as the 9th century. Goryeo's name was a continuation of Goguryeo (Koguryŏ) the northernmost of the Three Kingdoms of Korea, which was officially known as Goryeo beginning in the 5th century. The original name was a combination of the adjective go ("high, lofty") with the name of a local Yemaek tribe, whose original name is thought to have been either *Guru (溝樓, "walled city," inferred from some toponyms in Chinese historical documents) or *Gauri (가우리, "center"). With expanding British and American trade following the opening of Korea in the late 19th century, the spelling "Korea" appeared and gradually grew in popularity; its use in transcribing East Asian languages avoids the issues caused by the separate hard and soft Cs existing in English vocabulary derived from the Romance languages. The name Korea is now commonly used in English contexts by both North and South Korea.
In South Korea, Korea as a whole is referred to as Hanguk (한국, [haːnɡuk], lit. "country of the Han"). The name references Samhan, referring to the Three Kingdoms of Korea, not the ancient confederacies in the southern Korean Peninsula. Although written in Hanja as 韓, 幹, or 刊, this Han has no relation to the Chinese place names or peoples who used those characters but was a phonetic transcription (OC: *Gar, MC Han or Gan) of a native Korean word that seems to have had the meaning "big" or "great", particularly in reference to leaders. It has been tentatively linked with the title khan used by the nomads of Manchuria and Central Asia.
In North Korea, Japan, China and Vietnam, Korea as a whole is referred to as 조선, (Joseon, [tɕosʰʌn]), 朝鮮 (Chōsen), 朝鲜/朝鮮 (Cháoxiǎn/Jīusīn), Triều Tiên (朝鮮) lit. "[land of the] Morning Calm"). "Great Joseon" was the name of the kingdom ruled by the Joseon dynasty from 1393 until their declaration of the short-lived Great Korean Empire in 1897. King Taejo had named them for the earlier Kojoseon (고조선), who ruled northern Korea from its legendary prehistory until their conquest in 108 BCE by China's Han Empire. This go is the Hanja 古 and simply means "ancient" or "old"; it is a modern usage to distinguish the ancient Joseon from the later dynasty. Joseon itself is the modern Korean pronunciation of the Hanja 朝鮮 but it is unclear whether this was a transcription of a native Korean name (OC *T[r]awser, MC Trjewsjen) or a partial translation into Chinese of the Korean capital Asadal (아사달),  whose meaning has been reconstructed as "Morning Land" or "Mountain".