The Cold War was a period of geopolitical tension between the United States and its allies, and the Soviet Union and its allies, which began after the end of World War II. The primary ideological conflict during the Cold War was between capitalism and communism. The United States viewed communism as a threat to its security, as it believed that communism was spreading and that it could eventually lead to a global revolution against capitalism. The United States also feared that the Soviet Union would use its nuclear weapons to attack the United States or its allies. In response to this threat, the United States developed a policy of containment, which aimed to prevent the spread of communism and weaken the Soviet Union. The United States also developed a strategy of deterrence, which aimed to prevent the Soviet Union from attacking the United States or its allies by threatening to retaliate with nuclear weapons. The Cold War ended in 1991 with the collapse of the Soviet Union.