Final answer:
The invasion led to U.S. and UN involvement in Korea to counter the spread of communism, marking the start of the Korean War and highlighting Cold War tensions.
Step-by-step explanation:
The invasion of North Korea into South Korea on June 25, 1950, prompted a significant international response. President Truman, concerned with the spread of communism and protecting U.S. interests in Asia, particularly Japan, leveraged the domino theory and approached the United Nations for assistance. The United Nations Security Council condemned North Korea's aggression and, due to the Soviet Union's boycott of UN meetings, passed a resolution to support South Korea without a Soviet veto.
The rapid advancement of the North Korean forces, supplied with Soviet equipment and tactics, and their successful capture of Seoul lead to a multination coalition, led predominantly by the United States and UN forces, to intervene militarily. This marked the beginning of the Korean War, a conflict that would last until 1953 and set the tone for Cold War dynamics in Asia. It was a practical example of the containment policy of the United States aimed at curbing the spread of communism.