25th June 1950: Korean War begins when North Korean forces cross the 38th parallel

Korea had been under Japanese occupation from 1910 until Japan’s defeat in 1945. Following the war, Korea was divided along the 38th parallel with the Soviet Union occupying the north, and the United States occupying the south. This division was intended to be temporary, but in 1948 the capitalist Republic of Korea was established in the south under Syngman Rhee, while Kim Il-sung led the communist Democratic People’s Republic of Korea in the north.
By 1949, hostilities were simmering along the border, while both North and South Korea received military support from their allies. On June 25, 1950, these tensions erupted into full-scale war. North Korean troops launched a surprise invasion under the pretext of the south having attacked first. The North quickly advanced southward and captured Seoul, the capital of South Korea, within days.
The United Nations, led by the USA, responded swiftly to the invasion. With the Soviet Union boycotting the UN Security Council over Taiwan’s occupation of China’s permanent seat, on June 27, 1950, a resolution was passed calling for member states to assist South Korea. President Harry S. Truman authorised U.S. military intervention, and soon UN forces from 21 countries were deployed to the Korean Peninsula, with American troops making up 90% of these.
The early months of the war were marked by dramatic shifts between the two sides but, following China’s entrance into the war in October 1950, the war became brutal and bloody stalemate. An armistice agreement was eventually signed on July 27, 1953, but the Korean peninsula remains divided to this day.