What was president Eisenhower's explanation of the domino theory?

If one country falls to communism, the communists will know that they can succeed; and if they see that the US cannot, or will not intervene, then they will know that they might succeed with another country...and then another one, and so forth. Eisenhower explained the domino theory , in which he likened the countries on the brink of communism to a row of dominoes waiting to fall one after the other. "You have a row of dominoes set up," the president said. "You knock over the first one, and what will happen to the last one is the certainty that it will go over very quickly."