What is the common factor shared by these famous South Carolinians?

Reasoning based on the ease with which we can bring something to mind involves the use of the heuristic

What was the name of the theory that said that if one country in a region fell to communism, others would surely follow? 1) domino theory 2) arms race 3) brinkmanship 4) containment theory

Why would someone who is studying the history or culture of this time. find this text interesting important or useful?