Cold War
After the United States had invaded Cuba and failed in the Bay of Pigs, the Soviet Union attempted to supply Cuba with nuclear missiles. The missiles in Cuba would have allowed the Soviet Union to target almost the entire United States effectively. In response the United States sent a large number of ships to blockade Cuba to prevent the Soviet Union from sharing the weapons. The United States and Soviet Union agreed that the Soviet Union would no longer give nuclear weapons to Cuba if the United States didn't invade Cuba again. That was the highest period of tension during the Cold War and was the closest the world came to a nuclear war, with possible global conflict to follow.