The domino effect is a theory that suggests that one event sets off a chain reaction of similar events, particularly in political contexts. In the case of the 1989 revolutions in Eastern Europe, this concept illustrates how the fall of one communist regime inspired others to rise up and challenge their governments, leading to widespread changes across the region. The interconnectedness of these movements demonstrated how the actions in one country could significantly influence neighboring countries and contribute to a larger wave of democratic change.