The correct answer to this open question is the following.
The Korean War, Cuban Missile Crisis, the Vietnam War, and the Watergate scandal were all key events that took place during the Cold War era. These events had the most significant impact on the United States society and policy because it caused the United States government to make decisions and implement changes in the domestic policy as well as the foreign policy to try to contain the advancements and movements of the Soviet Union.
During the Cold War years, the United States and the Soviet Union competed almost in everything, basically in the arms race, the space race, and the spread or containment of Communism, respectively. These caused too many problems and tension not only between the two but to all the countries. Ket's just remember that during the Cuban Missiles Crisis of October 1962, the world was on the brink of another major war.