“If the best minds in the world had set out to find us the worst possible location in the world to fight this damnable war,” U.S. Secretary of State Dean Acheson once said, “the unanimous choice would have been Korea.”
Since the beginning of the 20th century, Korea had been a part of the Japanese empire, and after World War II it fell to the Americans and the Soviets to decide what should be done with their enemy’s imperial possessions. In August 1945, two young aides at the State Department divided the Korean peninsula in half along the 38th parallel. The Russians occupied the area north of the line and the United States occupied the area to its south.
North Korea invaded South on June 25, 1950, opening the conflict. Under the UN banner, President Harry Truman ordered American forces to the peninsula. Initially the North Koreans overwhelmed their neighbors and forced them into a small area around the port of Pusan. While fighting raged around Pusan, UN commander General Douglas MacArthur masterminded a daring landing at Inchon on September 15, shattering the North Korean offensive and driving them back over the 38th Parallel.
Though China had been warning of intervention for much of the fall, MacArthur dismissed the threats. In October Chinese forces crossed the Yalu River and entered combat. The next month, they unleashed a massive offensive which sent UN forces reeling south after engagements like the Battle of Chosin Reservoir. Forced to retreat to the south of Seoul, MacArthur was able to stabilize the line and counterattacked in February. Re-taking Seoul in March, UN forces again pushed north. On April 11, MacArthur, who had been clashing with Truman, was relieved and replaced by General Matthew Ridgway. Pushing across the 38th Parallel, Ridgway repelled a Chinese offensive before halting just north of the border.
With the UN halt north of the 38th Parallel, the war effectively became a stalemate. However serious fighting still took place with the Battles of Heartbreak Ridge, White Horse, Triangle Hill, and Pork Chop Hill.
The negotiations at Panmunjom finally bore fruit, and an armistice went into effect on July 27, 1953. No formal peace treaty has ever been concluded.
Information from The Korean War: The Forgotten Conflict, by Kennedy Hickman on About.com.