What is domino affect?

Answer 1

The domino Effect is a phenomenon where a chain of consequences is created by a single event. As in a line of dominos, where 1 domino is struck, others fall as a consequence of the original action.

As it pertains to the Vietnam War, the domino effect was the theory that the US government used to justify its intervention in Vietnam. The position of the pro-war, anti-communist advisers in the government was that if Vietnam was allowed to "fall" to communism, this would set off a 'domino effect' whereby first neighboring countries such as Laos, Cambodia and Thailand would fall into communist revolution, and by extension countries further afield would be overtaken as the global communist revolutionary movement gained momentum. According to this line of thinking, to stop communism in Vietnam was to stop the world from falling into communist control.

This theory is disproved, as we know Communist North Vietnam defeated US forces, but this did not result in a domino effect of neighboring countries becoming communist.