In Cold War US history there is an era of foreign policy called Containment policy. The idea was put forth by George Kennan, Secretary of State during 1947 under Harry Truman’s Administration. Kennan had sent a multi-page telegraph to the President, warning about the Soviet expansion into Europe and the Middle East.
Containment was successful in some ways and a failure in others. You have two major tests of the policy in the first 8 years following the end of World War II including the overtaking of China by Mao Zedong’s Communist Party. The United States had supported the Nationalists of China and Jiang Jieshi during World War II, however Mao Zedong had defeated the Nationalist forces in 1949. After that you have the Nationalists fleeing to Taiwan. Today China refuses to recognize Taiwan as its own nation but as a part of China. This was viewed as a major failure of Containment Policy for the West because China has become Communist, meaning 25% of the world’s population was now Communist.
Of course there was a success of Containment and that was in the Korean War. In 1950, after America had pulled a large number of troops out of Korea when the nation was deemed outside of America’s defense perimeter, 300,000 Chinese troops crossed the Yalu river and the UN troops retreated across the 38th Parallel. UN troops were forced to retreat and the North Korean and Chinese troops almost took over the whole country. Soon after you’ll have President Truman issue NSC-68 which quadrupled the size of the defense budget and created an enormous military for the war. After, US and UN troops fight back the Chinese and North Koreans to the 38th Parallel where the border remains today. This result was seen as a victory for Containment policy as it had accomplished its go keeping Communism at bay and contained and stopping it from spreading to South Korea.