The correct response is:
The domino theory describes the U.S. policy for stopping the Soviet Union from influencing other countries in which people were staging revolutions and independence movements.
The domino theory was a key rationale for U.S. involvement in global conflicts during the Cold War, positing that if one country fell to communism, neighboring countries would likely follow suit, leading to a "domino effect." Thus, the U.S. sought to prevent the spread of communism through military and political means during various revolutions and independence movements.