Does momentum matter in global affairs? If one country falls to hostile forces, will others follow?
The domino theory — the idea that setbacks can accumulate quickly and catastrophically — is one of the most controversial ideas in U.S. foreign policy. It guided a half-century of statecraft during the Cold War, only to be rejected by many historians of that conflict. But the anniversary of the Korean War, which began 70 years ago on June 25, 1950, reminds us that the domino theory was rooted in key realities of international affairs. And it alerts us that domino dynamics could affect U.S.-China competition today.
The domino theory became infamous thanks to the Vietnam War, which the United States fought in part to prevent the rest of Southeast Asia from falling. U.S. President Dwight D. Eisenhower coined the phrase in 1954, in explaining why losing Indochina would be so disastrous: “You have a row of dominoes set up, you knock over the first one, and what will happen to the last one is ... it will go over very quickly.” Beyond Vietnam, the idea that one defeat could trigger others was ubiquitous during the Cold War.