The Domino Theory is a simple rhetorical device. Policymakers used it to simplify their worries about the expansion of communism and justify the global strategic significance of small countries like Vietnam, Laos, and Cambodia to the American public.

It’s far too simplistic. Therefore I think it’s best not to think in absolute terms of ‘right’ or ‘wrong’ — that will simply lock you into an outmoded debate. This is a frequent tact taken by historians and commenters on AskHistorians. They offer valid critiques that challenge the monolithicism of communism, but too often this impulse leads them to push their critiques too far, arguing against any connection or dependance among communist movements. If proponents of the original theory see the dominos falling in a straight line, some of their critics tend to pick up the dominos and scatter them about, telling us there’s no connection at all.

Yet with time and the opening of archives, we’ve arrived at a more complex picture. For example, Bruce Cumings wrote a very interesting history of the Korean War that placed an emphasis on Korean actors and a pre-existing civil conflict among them. This led him to argue that Kim Il-Sung and the DPRK were acting on their own when they invaded the ROK/South Korea in 1950, and that their calculations were separate from the Cold War. When Chinese and Soviet archives opened, however, we learned that the DPRK indeed had sought out Mao and Stalin’s approval before they dared launch the attack.

Similarly for Vietnam, western writers have looked for ‘missed opportunities’ to argue that the threat of communist expansion only existed because of American or European errors. Many people confidently assert that Ho Chi Minh only chose communism because the United States and France did not support the Democratic Republic of Vietnam (DRV). Thus the domino theory and the entire premise of communism was one big illusion, or even one big lie. This however is easily rebutted now, and a basic biography of Ho shows his long commitment to both international communism and nationalism. (For a recent example of this 'missed opportunities' de-communization of Ho, see Fredrik Logevall's Pulitzer winning Ember's of War)

Rather than that path, we can think about why this concept appealed to Washington and why it seemed credible. There were close connections between the communist leadership of these countries, particularly in Indochina (which was the area Eisenhower referenced when he first invoked ‘dominos’). No other than Ho Chi Minh had been the USSR Comintern’s point man in the 1930s for the organization of SE Asian communist parties. Ho and the Indochinese Communist Party also had a longstanding relationship with the Chinese communists, that proved pivotal after 1949. The DRV was on the verging on defeat in 1949. But Mao’s victory in the Chinese civil war opened the border between his and Ho’s forces allowing Chinese weapons, materiel, and advisors to assist the DRV. At the end of the war, China and the USSR would also play an important role encouraging the DRV to accept the division of Vietnam at the Geneva Accords.

In turn, the Vietnamese advisors and soldiers organized Lao and Khmer subordinated allied forces, and did much of the fighting themselves in Laos and Cambodia. Because of their long colonial connection, and much like the French, Vietnamese communists saw Indochina as one battlefield and political space in which to spread revolution. The Geneva Accords halted these close contacts for a time, but they were renewed during the Second Indochina War, when the DRV likewise went about organizing and supporting resistance in Laos and Cambodia (though they struggled to control the new Khmer Rouge organization). Hanoi did, and still does, hold a great deal of influence over the Lao socialist government. And while the DRV-Democratic Kampuchea (Khmer Rouge) relationship fractured violently, remember that Vietnamese occupied Cambodia for the next decade and had its own network of Cambodians that it could draw on after expelling the Khmer Rouge. The current autocrat in Cambodia, Hun Sen, was one of these people.

Thus, Laos and Cambodia did end up controlled by Socialist governments subordinate to Vietnam. Policymakers were not wrong in seeing connections between Moscow-Beijing and communist parties, nor in the connections between smaller Asian communist parties. There was a connection between Chinese support, the growth of the DRV, and the expansion of the Indochina War into Laos and Cambodia. But it was the close relationship between the three countries, and the historic domination of Vietnamese in colonial and anti-colonial circles, that produced this complicated and intertwined outcome. It would not, for example, apply in the Philippines or Indonesia. The relationships between the communist parties were not monolithic, they varied widely. They certainly did not progress in a determined, gravitational fashion, even in Indochina.