What was the domino theory?

The domino theory was a theory prominent from the 1950s to the 1980s, that speculated that if one country in a region came under the influence of communism, then the surrounding countries would follow in a domino effect. The domino theory was used by successive United States administrations during the Cold War to justify the need for American intervention around the world.

It speculated that if one country in a region came under the influence of Communism then the surrounding countries would follow the domino effect