The domino theory justifies US military presence in Vietnam - communist victory there would cause surrounding countries to fall.
Vietnam fell in 1975. Most predicted dominoes did not follow. The domino theory oversimplified revolutionary nationalism as monolithic communist expansion.
What changed?
By 1969, the domino theory had been American foreign policy orthodoxy for fifteen years and social studies curriculum for nearly as long. Nixon inherited it along with 543,000 American troops. His response was Vietnamization, training South Vietnamese forces to fight their own war while American troops withdrew, which required the theory to remain true even as its application changed. The dominoes would still fall without American support; they would simply be held up by South Vietnamese hands instead.
The draft lottery began on December 1, 1969, the first such lottery since World War II. A fishbowl held 366 blue capsules, one for each day of the year, and capsules were drawn one by one to determine the order in which young men would be conscripted. Students who had been taught the domino theory in civics class were now learning their draft numbers. The abstraction had become personal.
The theory's evidence base had always been shakier than its official confidence implied. Nikita Khrushchev and Mao Zedong had been in open ideological conflict since the late 1950s, international communism was not the unified project the domino model required. Vietnam's revolutionary movement drew on deep nationalism and grievances against French colonialism that existed entirely independently of Moscow's agenda. These complications were available to scholars; they rarely reached the textbook.
Saigon fell on April 30, 1975. The domino had toppled. Cambodia fell to the Khmer Rouge. Laos fell to the Pathet Lao. And then the cascade stopped. Thailand did not fall. Malaysia did not fall. The Philippines did not fall. Vietnam and Cambodia, far from acting as partners in a communist project, went to war with each other in 1978, with Vietnam invading Cambodia and China attacking Vietnam.
The dominoes had been made of different materials all along. They had their own weights, their own histories, their own reasons to stand or fall. The metaphor had never described the actual politics of Southeast Asia. It described the anxieties of Washington.
