On June 25, 1950, Soviet Union–backed North Korea invaded U.S.-backed South Korea, sending its forces across the agreed boundary at the thirty-eighth parallel in an attempt to bring the entire peninsula under its control. When UN Secretary-General Trygve Halvdan Lie received the news, he reportedly replied, “This is war against the United Nations.” At the United States’ request, he convened the UN Security Council the next day. The council quickly passed Resolution 82, which called for the “immediate cessation of hostilities” on the peninsula. Two days later, the council passed Resolution 83, which authorized the use of force to “repel the armed attack.”

After several weeks of fighting, UN and South Korean forces were defending an area called the Pusan perimeter, a zone of southeastern South Korea around the Port of Pusan, against North Korea’s southward advance. General Douglas MacArthur, an American commanding U.S. and allied forces as part of the UN mission, was also making plans for a landing at Inchon, near the South Korean capital, Seoul.

A successful Inchon landing would mean the prospect of swiftly liberating South Korea. The Security Council faced a weighty related decision. Should the United Nations simply call for the restoration of the prewar status quo, pushing North Korea’s military back to the thirty-eighth parallel? Or should UN forces advance into North Korea and try to unify the peninsula?

A UN move into North Korea would bring the risk of war with China, the Soviet Union, or both. At the same time, it would carry the possibility of a peaceful and unified peninsula. Merely restoring the status quo would reduce the risk of war among global powers. It would also preserve the hostile North Korean leadership and leave the divided peninsula as an open wound, and potential battleground, in the intensifying Cold War.