During the first battle of the korean war in june of 1950,
the united nations pledged to come to the aid of north korea.
south koreans crossed the 38th parallel and continued into north korea.
the soviet union marched on south korea and captured it within days.
north koreans took control of the south korean capital of seoul.

It was the first battle that made the US interfere in the war and the invasion was made by the North supported by the Soviet Union, although it didn't directly do anything. In the end what happened was that:

North Koreans took control of the South Korean capital of Seoul.

kennedy used a range of this to develop a 'flexible response' plan for any international crisis. “he also expanded the it was important, because it ordered the fall of khruschev.