In 1950, the Korean War broke out. The offensive of the North Korean People's Army was quite fierce, and the Rhee clique in South Korea was overwhelmed and rushed to the United States for help. After the outbreak of the Korean War, Chiang Kai-shek immediately decided to send the 52nd Army to the aid of South Korea. And reported the situation to Acheson of the United States.
Truman, who was president of the United States at the time, heard the news that Chiang Kai-shek was ready to support South Korea, and his first reaction was to "thank Chiang Kai-shek for his kindness" and called on more allies to actively participate in the "action against North Korea." And General MacArthur, the five-star U.S. general in charge of South Korea's security at the time, saw the overwhelming attack of the Korean People's Army on South Korea and wanted Truman to agree to Chiang Kai-shek's request.
However, the State Council headed by Acheson resolutely opposed Chiang Kai-shek's dispatch of troops, because once Chiang Kai-shek sent troops to Korea, China would certainly not sit idly by and would certainly redouble its blows against the "United Nations Army." Most importantly, Chiang Kai-shek's troops were likely to expand the scale of the Korean War, and it would be difficult to control the situation at that time, thus triggering a third world war, which the United States did not want to see.
In fact, Truman's heart was originally inclined to Chiang Kai-shek's invasion of Korea, but when he heard Acheson's threatening opposition, he was afraid that Chiang Kai-shek's invasion of Korea would really lead to the intervention of the Chinese Communists, so he submitted to Acheson's proposition. So in the end, Truman agreed to Acheson's proposal and refused Chiang Kai-shek's request to invade Korea.