During the cold war, the united states was involved in certain regional conflicts due to fears later called the domino theory. which answer describes this concept?

if one nation in a region became communist, others nearby would quickly fall to communism.

if one nation in a region became communist, it would make no difference.

if one nation in a region became communist, their neighbors would fight them.

if one nation in a region became communist, it would force its citizens to seek safety in nearby countries.

The domino theory or also called snowball effect sequence applied to international politics according to which, if a country enters a certain political system, it would drag others from its area towards that same ideology. This theory is often attributed to President Eisenhower who predicted that communism could expand throughout the world if the spiral could not be stopped. Because of this the correct answer is the first option: If one nation in a region became communist, others nearby would quickly fall to communism.

Explanation:

After the War, the USSR had pledged to hold elections in the nations occupied to decide their governments; but these elections were sometimes not held. In this way, Albania and Yugoslavia joined the nations invaded by the USSR while in Asia the communist North Korea threatened to drag its neighbor from the South.  This seemed to indicate that, despite the apparent American superiority, there was a certain contagion from one country to another, contagion that threatened to surround the entire United States of communist countries.