The 5 main countries involved (not to take away from the other nations whose citizens took part in the UN's police action) each had their own reasons for fighting the Korean War. Kim Il Sung, leader of the communist North Koreans, declared war at 11:00 a.m. on 25 June, 1950, some 7 hours after his forces crossed the 38th parallel into South Korea. His goal was to unite the Korean Peninsula under the rule of the Korean Communist Party. South Korea was fighting for the survival of its fledgling democratic society. Communist China engaged UN forces to keep North Korea intact as a communist nation, probably to act as a buffer between it and the US supported Republic of Korea. The United States had as its stated objective a return to the status quo ante, in other words, to push the invaders back across the 38th parallel. In so doing, the US hoped to deter the domino effect and halt the spread of communism in Asia. The Soviet Union did not take an active part in the hostilities, but it did supply advisors and equipment to the North Koreans. Their purpose was probably to observe US doctrine and hope for a weakening of the US, militarily, politically and economically.
These were the initial goals. The initial goals played a great role on the Korean war, obviously.
These were the initial goals. The initial goals played a great role on the Korean war, obviously.