On 12 January 1950, Acheson gave a speech before the National Press Club, in which he proclaimed that “a new day … has dawned in Asia.” This was three months after China had fallen to Communist insurgents armed by Moscow.
The U.S. “defensive perimeter,” announced Acheson, had now shrunk to include only Alaska’s Aleutian Islands, Japan (including Japan’s Ryukyu Islands, which extend from within 50 miles of South Korea to 67 miles of Taiwan), and the Philippines. Regarding South Korea, Taiwan and Southeast Asia, he said, “no person can guarantee these areas against military attack.” Disingenuously, he added, “one hesitates to say where such an armed attack could come from.” Acheson lumped all the rest of Asia together with Communist China as “the Asian peoples,” whom he said were “on their own.” He said all previous east-west relations (which he characterized as “paternalism” or “exploitation”

were over. Then he added some very confusing language, saying of “the Asian peoples,” that “We are their friends. Others are their friends.” As to whether Acheson meant to include the Soviet Union among “the Asian peoples,” or among the “others” who were their "friends,” he was perhaps intentionally ambiguous.
The policy Acheson put forward in this speech had been formulated at a State Department meeting in October 1949 [corrected date], immediately following the fall of China. (For more detail, see Evans’
Blacklisted by History, particularly chapter 31, “A Conspiracy So Immense.”

The meeting was convened by Ambassador at Large Philip Jessup, director of the Research Committee of the Institute of Pacific Relations, which would be identified in a report of the Democrat-controlled McCarran subcommittee as "a vehicle used by the Communists to orient American far eastern policies toward Communist objectives."
Aside from being Acheson's top adviser on the Far East, Jessup was a long-time intimate collaborator with Frederick Vanderbilt Field, who had publicly identified himself as a “Communist” in the CPUSA’s official organ,
Political Affairs, in January 1949. Field had also been identified in 1938 by Whittaker Chambers (and would later be independently identified by Elizabeth Bentley and Louis Budenz) as a member of the Communist underground, affiliated with the GRU
apparat.
For more on this, see Edward M. Collins,
Myth, Manifesto, Meltdown: Communist Strategy, 1848–1991; Lauren Kessler,
Clever Girl: Elizabeth Bentley, the Spy Who Ushered in the McCarthy Era; or especially
Blacklisted by History, chapter 30, “Dr. Jessup and Mr. Field.”