Marine infantrymen take cover behind a tank while it fires on Communist troops ahead. Hongcheon Area, May 22, 1951.

The Korean War started on June 25, 1950 with the forces of the Democratic People's Republic of Korea (DPRK and commonly known as North Korea) invading the south without much warning.

In the years following the surrender of Japan and Germany heralding the end of the Second World War, there were numerous political upheavals : the Cold War is said to have started in 1946 with numerous KGB agents found to be integrated into the American and Canadian populations, previously colonized countries like India (Britain) gained independence and partition into two modern day Pakistan, Bangladesh and India in 1947, Indonesia (Netherlands)gained independence after fighting the Dutch in 1947 as well, and then China had the People's Revolution bringing in the communist era in China in 1949, to name just a few. The situation on the Korean peninsula was similar to what happened in Germany with the Russians and Americans meeting halfway, in Korea's case around the 38th parallel after General MacArthur's forces drove the Japanese out of Korea, ending 35 years of Japanese colonial rule in Korea. Thereafter, two separate governments were set up in Korea, both claiming to be the legitimate government. This naturally created tensions in Korea, with the Russians maintaining some influence and when China turned communist, the DPRK (North Korea) was already firmly in the grip of Marxist ideology and at odds with the South, which was trying to rebuild with a more Western style of market economics and capitalism. The South, or Republic of Korea (ROK) was firmly anti-communist and sided with the Americans in the new Cold War.

After an initial push by the North Korean army throughout July and August 1950, the South's army was pushed back to the Nakdong River valley, in which Daegu is situated. The South knew the river was virtually their last line of defense before they would be pushed to the Busan and have lost the war. In mid-September, as the North's army prepared for a big offensive, UN forces, mostly American Marines under the command of General MacArthur, landed at Incheon and with superior air power and plenty of weaponry leftover from their defeat of Japan and their continuing presence in the area, gained Incheon and Seoul and began cutting off the North's supply lines, causing a rapid retreat back toward the 38th parallel. The decision to continue pushing into North Korea was both influenced by the Truman doctrine of opposition to Communisism wherever it existed in the world, and the issue of POW's. Together, the Americans and the South's armed forces succeed in pushing the North back to within about 100 km of the Chinese border. China got involved mainly from concern that once the UN forces had contained the North, they might push further into China, which being a new communist state was not going to take that chance. So China, sending in vast numbers of troops to aid their comrades in the North, and essentially turned the tide of the war. Their surprise tactics are well documented. For most of 1951 and 1952, the bloody war see-sawed back and forth over the 38th parallel, decimating whatever historical architecture Korea had left after their long colonization by Japan.

Peace negotiations began early in 1951, with a major issue being the repatriation of POW's. In the meantime combat continued. The Chinese requirement was that the majority of POW's repatriate to the North. However, most of them wanted to go to the South. Finally on July 27, 1953, the communists had given up this condition and India's suggestion at the United Nations of an armistice was accepted, and hostilities ended. As of this date, no peace treaty has been signed. The front line at that time was made into the current DMZ Demilitarized Zone, protected on one side by the North's military and on the other by the South and the Americans. To the east, the DMZ extends somewhat north of the 38th parallel and to the west, a little south of it. The city of Gaeseong, where the armistice was signed, was originally a part of the south, but now is a well-known city in the north. It is also the site of current peace negotiations and family reunion discussions between the North and South.

To this day, there are some Koreans who think that Japan bears some culpability in the division of the peninsula, because of their long colonization of Korea, and the resulting division of the peninsula in 1948, as a direct result of the start of the Cold War.