From Embers of War: The Fall of an Empire and the Making of America's Vietnam, by Fredrik Logevall (Random House, 2012), Kindle pp. 290-293:
BROADER INTERNATIONAL DEVELOPMENTS ALSO SHAPED ACHESON’S thinking on Vietnam in 1949. He began to pay more attention to Southeast Asia’s economic potential, particularly in terms of facilitating Japan’s recovery. Given the instability in China, Washington planners deemed it absolutely essential to secure a stable, prosperous Japan under U.S. control. Southeast Asia, rich in rice, tin, oil, and minerals, and with a population of 170 million (bigger than the United States), could play a principal role in this endeavor. George F. Kennan, head of the Policy Planning Staff, influenced Acheson in this direction, as did the young Dean Rusk, deputy undersecretary of state and a man Acheson asked to take on a larger role in Asian policy. The maintenance of a pro-Western Southeast Asia, they and other government analysts argued, would provide the markets and resources necessary for Japan’s economic revival—and help the recovery of Western Europe (by then well under way, but showing signs of a slowdown) as well. According to Rusk, the importation of rice from Indochina, for example, could be a terrific boon in securing Japan’s revitalization.
Then, in the second half of the year, came two momentous developments: In August, the Soviet Union for the first time detonated an atomic device; and in September, Mao Zedong’s forces completed their rout of Chiang Kai-shek’s Guomindang. Specialists had known that it was only a matter of time before Stalin got the bomb, but most thought the time would be the early or mid-1950s, not August 1949. The implications were huge (if not quite as enormous as some doomsayers in Washington proclaimed). It meant the end of the U.S. atomic monopoly and immediately raised fears that Stalin might embark on an aggressive course to expand his global reach. That worrisome thought only gained more currency the next month, when Mao Zedong consolidated his victory in China. Here neither the event nor the timing was a surprise to specialists—Nanjing had fallen in April, Shanghai in May, and Changsha in August—but for ordinary Americans it was sobering to hear Mao dramatically declare, from the Gate of Heavenly Peace in Beijing, the founding of the People’s Republic of China (PRC). Chiang and the remnants of his army fled to Formosa (now Taiwan).
Though some senior U.S. officials, Acheson among them, believed that the USSR and Mao’s government would ultimately experience a rift, in the short term the dangers seemed all too real. Instantly, the number of major Communist foes had doubled. As a report by the National Security Council (NSC) had put it in June, “the extension of Communist authority in China represents a grievous political defeat for us.… If Southeast Asia is also swept by Communism, we shall have suffered a major political rout the repercussions of which will be felt throughout the rest of the world, especially in the Middle East and in a then critically exposed Australia.… The colonial-nationalist conflict provides a fertile field for subversive Communist movements, and it is now clear that Southeast Asia is the target for a coordinated offensive directed by the Kremlin.”
There was in fact no such coordinated offensive. Stalin’s interest in Southeast Asia remained minimal, it was soon clear, and his feelings about the Chinese developments were decidedly mixed. Still, U.S. leaders could be forgiven for thinking that Communism was on the march in the region. In addition to Mao in China and Ho in Vietnam, there were Communist-led rebellions in Indonesia, in newly independent Burma, in Malaya, and in the Philippines. All four rebellions would fail in due course, but in late 1949 their mere existence fueled American fears. Did the historical momentum now lie with the Communists? Even if it didn’t in objective terms, might the perception gain hold that it did, producing a bandwagon effect that could have a pernicious impact on American national security interests? It seemed all too possible.
The NSC report, with its warnings of the far-reaching consequences—the Middle East! Australia!—of a loss of Southeast Asia, was an early version of what would come to be known as the domino theory. Knock over one game piece, and the rest would inevitably topple. For the next twenty-five years, high U.S. officials, on both the civilian and the military sides, in both Republican and Democratic administrations, linked the outcome in Vietnam to a chain reaction of regional and global effects, arguing that defeat in Vietnam would have calamitous consequences not merely for that country but for the rest of Southeast Asia and perhaps beyond. Though the nature and cogency of the domino theory shifted over time, the core claim remained the same: If Vietnam was allowed to “fall,” other countries would inevitably follow suit.