Even so, the North Korean invasion came as an alarming surprise to American officials. As far as they were concerned, this was not simply a border dispute between two unstable dictatorships on the other side of the globe. Instead, many feared it was the first step in a communist campaign to take over the world. For this reason, nonintervention was not considered an option by many top decision makers. (In fact, in April 1950, a National Security Council report known as NSC-68 had recommended that the United States use military force to “contain” communist expansionism anywhere it seemed to be occurring, “regardless of the intrinsic strategic or economic value of the lands in question.”)
“If we let Korea down,” President Harry Truman (1884-1972) said, “the Soviet[s] will keep right on going and swallow up one [place] after another.” The fight on the Korean peninsula was a symbol of the global struggle between east and west, good and evil. As the North Korean army pushed into Seoul, the South Korean capital, the United States readied its troops for a war against communism itself.
At first, the war was a defensive one–a war to get the communists out of South Korea–and it went badly for the Allies. The North Korean army was well-disciplined, well-trained and well-equipped; Rhee’s forces, by contrast, were frightened, confused, and seemed inclined to flee the battlefield at any provocation. Also, it was one of the hottest and driest summers on record, and desperately thirsty American soldiers were often forced to drink water from rice paddies that had been fertilized with human waste. As a result, dangerous intestinal diseases and other illnesses were a constant threat.
By the end of the summer, President Truman and General Douglas MacArthur (1880-1964), the commander in charge of the Asian theater, had decided on a new set of war aims. Now, for the Allies, the Korean War was an offensive one: It was a war to “liberate” the North from the communists.
Initially, this new strategy was a success. An amphibious assault at Inchon pushed the North Koreans out of Seoul and back to their side of the 38th parallel. But as American troops crossed the boundary and headed north toward the Yalu River, the border between North Korea and Communist China, the Chinese started to worry about protecting themselves from what they called “armed aggression against Chinese territory.” Chinese leader Mao Zedong (1893-1976) sent troops to North Korea and warned the United States to keep away from the Yalu boundary unless it wanted full-scale war