Answer:
Domino Theory
Step-by-step explanation:
DOMINO THEORY fears that if one Southeast Asian country were to fall to communism many others would follow.
Domino Theory is a popular theory in the United States around the 1950s to the 1980s on the influence of the style of government of a certain country, particularly the powerful one, which is expected to affect the surrounding areas or countries and thereby eventually copying the same style of government.
Hence, in this case, the right answer is DOMINO THEORY.