On the 25th of June, 1950 ten divisions of the North Korean Army invaded South Korea. In its narrowest sense, the invasion marked the beginning of a civil war between peoples of a divided country. In a far larger sense, it represented a break in tensions between the two dominant power blocs that had emerged from the Second World War (Quick Magazine June 25, 1950). Truman stated "In Korea the Government forces, which were armed to prevent border raids and to preserve internal security, were attacked by invading forces from North Korea. The Security Council of the United Nations called upon the invading troops to cease hostilities and to withdraw to the 38th parallel. This they have not done, but on the contrary ave pressed the attack." (Truman June 27, 1950). The main reason North Korea decided to invade South Korea was because North Korea became a Communist State in 1945, when the United States was finishing the War with Japan, the Soviet Union took Manchuria and entered North Korea. It was impossible for U.S. troops to get to Korea in time and fearing the Soviets would take the entire peninsula, War Department Colonels Charles H. Bonesteel and Dean Rusk hastily drafted an agreement which set out a demarcation line for the zones of influence for Korea marking the Soviet zone from the China/Russia border to end at the 38th parallel, while South of the 38th parallel would be the zone of influence for the United States. In the North, they were a Soviet-backed Democratic People’s Republic of Korea, and to the South a pro-Western Republic of Korea.
The countries that were involved in the Korean War were Soviet Union and People's Republic of China supporting North Korea. The countries that supported South Korea were Great Britain, United States and United Nations.