Timeline of events

North Korea’s Invasion and Retreat to Nakdong River (1950. 06. 25 ~ 09. 14)

Seoul fell to the Korean People’s Army(KPA) three days after the war broke out (June 28th). The United Nation Forces were dispatched (July 1st) to help South Korean forces but a month after the war began they were forced to retreat to the Nakdong River. The ROK Army and U.N. Forces desperately defended the Nakdong River line of defense for around 40 days (August 1st~September 14th) providing the foundation for the landing at Incheon and a counterattack.

Incheon Landing and Advance to Amnok(Yalu) River (1950. 09. 15 ~ 10. 24)

With the success of the landing at Incheon (September 15th) and the counterattack at the Nakdong River, the ROK Army and UN Forces were able to reclaim Seoul by September 28th as well as the 38th parallel within 15 days of launching the counteroffensive. On October 1st, the ROK and UN Forces crossed over the 38th parallel and within a month advanced up to Chosan near the Amnok River (October 1st~26th). Unification seemed to be within sight.

China’s Intervention, A New War (1950.10.25 ~ 1951.07.09)

As the ROK Forces advanced to the Amnok River(Chosan) by October 26th, 250,000 Chinese troops also crossed the river and were waiting for the troops to ambush them. Five large scale air-strikes by the Chinese forces, with the first launched on October 25th, continued until May of the following year. Because of the Chinese Army’s 2nd offensive in early December, the ROK and UN Forces had to retreat from Seoul on January 4th, just a month after capturing Pyongyang (December 4th) . They retreated further to the 37th parallel connecting Pyeongtaek and Samcheok. However, after recapturing Seoul on March 15th, the fighting continued mostly around the 38th parallel.

Ceasefire Negotiations and Continued Skirmishes Near the Military Demarcation Line (1951.07.10 ~ 1953.07.27)

The U.N. Forces and the Red Army began ceasefire negotiations on July 10th, 1951. However, during the negotiations which lasted for two years, South and North Korea continued fighting near the Military Demarcation Line to claim as much territory as possible. The two Koreas were separated by the Military Demarcation Line with the signing of the armistice on July 27th, 1953, three years after the breakout of war, and remain divided to this day.
Source : Data Source: ROK Army Military History Institute, Organized by the Korea Defense Daily, Edited by Jeon Ok-shin