When North Korean troops first crossed the 38th parallel—the two countries’ dividing line—South Korean troops scattered in disarray, and civilians streamed south. U.S. reinforcements initially failed to stem the tide, and the North Koreans pushed the coalition allies into the southeast corner of the peninsula, near Pusan.
Then UN forces under the command of General Douglas MacArthur turned the tide. While UN forces prepared to push north from Pusan, U.S. troops made a daring amphibious landing at the port of Inchon in September 1950. Supported by naval gunfire and air bombardment, the troops poured onto the beach, then threatened the enemy from behind. The North Koreans retreated north rather than risk being trapped in a closing vise.
Allied forces pursued the North Koreans all the way to the Yalu River, the border with China. Then, their border threatened, the Communist Chinese joined the fight. They sent more than a million troops in a ferocious counteroffensive that drove UN armies south again.
Meanwhile, MacArthur and President Truman came to a standoff. At issue was the popular general’s repeated defiance of the civilian president. In 1951, when MacArthur lobbied to expand the war into China, even at the risk of world war, Truman fired him.
Soon the line between the armies stagnated. Three years of brutal fighting left Americans divided over the war. An uneasy truce split the Korean peninsula into a Communist north and democratic south.