The correct answer is letter C
The Korean War was a conflict that took place between 1950 and 1953 between North Korea and South Korea and began when North Korean troops crossed the border separating Korea, starting the invasion of South Korea. This war was one of the first manifestations of bipolarization that characterized the world during the Cold War period.
Since the invasion of South Korea, the war can be divided into three distinct phases. The first phase took place between June and September 1950. North Korean forces took advantage of their greater military power and almost conquered the entire peninsula, isolating South Korean troops from the Pusan Perimeter.
The second phase was characterized by the predominance of South Korean forces with the massive entry of the American army into the conflict. This phase extended from September to October 1950 and began with the important action of the Americans in defense of the Pusan Perimeter. American troops were also important for the reconquest of South Koreans' territory, especially since the arrival of troops in Inchon.
The advance of American and South Korean troops over North Korean territory generated a response from China, which feared that American troops would invade its territory. China's entry into the Korean War started the third phase of the conflict. This phase extended until 1953 and was characterized by the balance of forces.
The long duration of this phase, the great wear and tear caused by the war and the few movements on the battlefield (the troops were close to Parallel 38) resulted in the negotiation of a truce in Panmunjom, which was officially signed on July 27, 1953. The truce - despite being negotiated as something temporary - ended the conflict.
Some border changes took place, and a demilitarized zone was established on the border between the two countries. The relationship between the Koreas remains tense today, however, international observers are optimistic about the possibilities of bringing the Koreas closer together in the future.