The Korean conflict is an ongoing conflict based on the division of Korea between North Korea (Democratic People's Republic of Korea) and South Korea (Republic of Korea), both of which claim to be the sole legitimate government of all of Korea. During the Cold War, North Korea was backed by the Soviet Union, China, and other communist allies, while South Korea was backed by the United States, United Kingdom, and other Western allies.

The division of Korea by the United States and the Soviet Union occurred in 1945 after the defeat of Japan ended Japanese rule of Korea, and both superpowers created separate governments in 1948. Tensions erupted into the Korean War, which lasted from 1950 to 1953. When the war ended, both countries were devastated, but the division remained. North and South Korea continued a military standoff, with periodic clashes. The conflict survived the end of the Cold War and is still ongoing. It is now considered one of the 10 frozen conflicts of the world and is considered one of the oldest, along with the Sino-Taiwanese conflict.

The U.S. maintains a military presence in the South to assist South Korea in accordance with the ROK–U.S. Mutual Defense Treaty. In 1997, U.S. President Bill Clinton described the division of Korea as the "Cold War's last divide". In 2002, U.S. President George W. Bush described North Korea as a member of an "axis of evil". Facing increasing isolation, North Korea developed missile and nuclear capabilities.

A period of heightened tension began in 2017, but in the following year North Korea, South Korea and the U.S. held a series of summits, which promised peace and nuclear disarmament. This led to the Panmunjom Declaration on 27 April 2018, when the North and the South agreed to work together to denuclearize the peninsula, improve inter-Korean relations, end the conflict officially, and move towards the peaceful reunification. In subsequent years, diplomatic efforts faltered and military confrontation returned to the fore.

The Korean border remains the most militarized private area in the world with the presence of the Korean People's Army in north; the Forces of the Republic of Korea and the United States Forces Korea (highlighted notably through the Combined Forces) in south and the presence of the forces of United Nations in the Korean Demilitarized Zone (JSA and Camp Bonifas).

Korea was annexed by the Empire of Japan on 22 August 1910, and ruled by it until 2 September 1945. During the Japanese occupation of Korea, nationalist and radical groups emerged, mostly in exile, to struggle for independence. Divergent in their outlooks and approaches, these groups failed to unite into a single national movement. Based in China, the Korean Provisional Government failed to obtain widespread recognition. The many leaders advocating for Korean independence included the conservative and U.S.-educated Syngman Rhee, who lobbied the U.S. government, and the Communist Kim Il Sung, who fought a guerrilla war against the Japanese from neighboring Manchuria.

Following the end of the occupation, many high-ranking Koreans were accused of collaborating with Japanese imperialism. An intense and bloody struggle between various figures and political groups aspiring to lead Korea ensued.

On 9 August 1945, as agreed by the Allies at the Potsdam Conference, the Soviet Union declared war on Japan and advanced into Korea. The U.S. government requested that the Soviet advance stop at the 38th parallel. The U.S. forces were to occupy the area south of the 38th parallel, including the capital, Seoul. This division of Korea into two zones of occupation was incorporated into General Order No. 1, which was given to Japanese forces after the surrender of Japan on 15 August 1945. On 24 August 1945, the Red Army entered Pyongyang and established a military government over Korea north of the parallel. American forces landed in the south on 8 September 1945, and established the U.S. Army Military Government in Korea.