The Cold War was a decades-long ideological and geopolitical struggle between the United States and the Soviet Union that began following World War II. Key events that deepened tensions included Stalin reneging on allowing free elections in Eastern Europe, the Berlin Blockade, McCarthyism in the US, and the space race highlighted by the launch of Sputnik. Major crises like the Cuban Missile Crisis brought the two superpowers to the brink of nuclear war. Throughout the Cold War both sides sought to spread their influence and contain the other through military alliances like NATO and the Warsaw Pact as well as policies like containment and détente.