Short answers, pulled from the story.
Korea is a peninsular region in East Asia consisting of the Korean Peninsula, Jeju Island, and smaller islands. It is bordered by China to the north and Russia to the northeast, across the Amnok and Duman rivers, and is separated from Japan to the southeast by the Korea Strait.
Korea has been politically divided at or near the 38th parallel since the end of World War II in Asia in 1945, when the Soviet Union and United States agreed to divide it into two occupation zones. The division was meant to be temporary, but in 1948 two separate governments, the DPRK and the ROK, were established with the backing of each power.
Korea is the modern spelling of Corea, a name attested in English as early as 1614 and derived from the ancient kingdom of Goryeo. Goryeo's name was a continuation of Goguryeo, the northernmost of the Three Kingdoms of Korea.
Sejong the Great, who reigned from 1418 to 1450 during the Joseon dynasty, personally created and promulgated Hangul, the Korean alphabet. His reign was a golden age of cultural and scientific advancement.
The Korean War was fought from 1950 to 1953, beginning in June 1950 when Soviet-backed North Korea invaded the South. More than 1.2 million people died, and the war ended with an armistice rather than a peace treaty, leaving the two governments officially still at war.
The Three Kingdoms of Korea were Goguryeo, Baekje, and Silla. Goguryeo controlled the northern half of the peninsula and Manchuria, while Silla and Baekje controlled the southern half, until Silla conquered Baekje and Goguryeo with Tang aid in 668 to form Unified Silla.