This would be achieved by making sure that your own side could strike back even after being attacked by nuclear weapons, so The USA then came up with the Polaris missile, which could be fired from nuclear submarines below the surface. This was a great advantage to the USA because it meant that they could fire at Russia without them realizing because it was undetectable. In A2 it mentions that in 1955 the Americans launched a nuclear-powered submarine, which was a major advantage for the USA because it could be cruising at high speeds below the surface for weeks and the enemy would know nothing about it. It also says that not long after the nuclear-powered submarines came the Polaris missiles, which could be fired from below the surface from the submarines. These two things caused a big change in the attitudes of the world leaders. Their main concern now was to prevent nuclear war, and the source says that everything else came second. This Polaris missile changed the whole strategy of the Cold War and the attitudes of the leaders in it. .
The island of Cuba lies about 90 miles off the USA coast. From 1952 to 1959 a dictator ruled it called General Batista, the USA supported him for most of that time. American companies controlled most of Cuba business, so as long as Cuba was at peace American business profited. So the USA supplied Batista with arms. However Batista's rule became more and more brutal so America stopped supplying arms in 1957. The USA wanted a more effective government so it encouraged a resistance movement led by Fidel Castro. In 1959, Castro overthrew Batista's government and became Cuban president; he had by then become Communist, which worried the Americans at all seen as they had been trying to stop the spread of communism Communism. So the friendly relations between USA and Castro didn't last for long. Castro began a series of reforms, which included nationalizing the industries, which were mostly American.