The Domino Theory was a metaphor for the spread of communism, as articulated by US President Dwight D. Eisenhower in an April 7, 1954 news conference. Eisenhower expressed concern that communism, which had already become established in China under Mao Zedong, could spread across Asia and even toward Australia and New Zealand:
"You have broader considerations that might follow what you would call the "falling domino" principle. You have a row of dominoes set up, you knock over the first one, and what will happen to the last one is the certainty that it will go over very quickly. So you could have a beginning of a disintegration that would have the most profound influences.
...Then with respect to more people passing under this domination, Asia, after all, has already lost some 450 million of its peoples to the Communist dictatorship, and we simply can't afford greater losses.
But when we come to the possible sequence of events, the loss of Indochina, of Burma, of Thailand, of the Peninsula, and Indonesia following, now you begin to talk about areas that not only multiply the disadvantages that you would suffer through loss of materials, sources of materials, but now you are talking really about millions and millions and millions of people.
Finally, the geographical position achieved thereby does many things. It turns the so-called island defensive chain of Japan, Formosa, of the Philippines and to the southward; it moves in to threaten Australia and New Zealand."
Eisenhower and later American leaders, including Richard Nixon, used this theory to justify US intervention in Southeast Asia, including escalation of the Vietnam War. Although the anti-communist South Vietnamese and their American allies lost the Vietnam War to the communist forces of the North Vietnamese army and the Viet Cong, the Domino Theory did not come into play in Asia. Australia and New Zealand never considered becoming communist states.