Prior to World War I and Japan's annexation of Korea, all of Korea had been unified as a single state for centuries, known previously as the Goryeo and Joseon dynasties, and the last unified state, the Korean Empire. After World War II and beginning in the Cold War, Korea was divided into two countries along the 38th parallel (now the Korean Demilitarized Zone). North Korea was administered by the Soviet Union in the years immediately following the war, with South Korea being managed by the United States. In 1950, North Korea invaded the South, beginning the Korean War, which ended in stalemate in 1953. Even after the end of the Korean War, reunification proved a challenge as the two countries became increasingly diverged at a steady pace. However, in the late 2010s, relations between North and South Korea warmed somewhat, beginning with North Korea's participation at the 2018 Winter Olympics in Pyeongchang County, Gangwon Province, South Korea. In 2019, South Korean president Moon Jae-in proposed reunification of the two divided states in the Korean peninsula by 2045.