During the Cold War, how were the policy of containment and the domino theory related?

Containment was the U.S. policy of stopping Communism from spreading. The domino theory held that if one country became Communist, neighboring countries might follow, like falling dominoes. The United States therefore feared that if containment failed, Communism could spread from country to country; this matches the choice saying countries would fall to Communism like dominoes.

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