1. The Korean War

This United Nations-sanctioned conflict between North and South Korea left millions of lives lost, the country devastated, and tensions between East and West heightened.

The Korean War marked an important shift in American foreign policy, as President Truman committed troops to the conflict without consulting Congress. This event led to a re-examination of the role of the United Nations and its ability to manage international affairs. It also brought about an increased reliance on nuclear deterrence, with the US embarking upon a massive arms race with the Soviet Union.