America had been highly influential in Cuba since the early 1900s. Much of Cuba's industry was owned by US business and its main export, sugar, was controlled by the USA.
In 1950s, Cuba was being led under the corrupt and oppressive military dictatorship of Fulgencio Batista. However he supported US interests on the island and hence, Washington supported him.
The Batista regime was extremely unpopular with the Cuban people. In 1956, Fidel Castro and Che Guevara gathered a force of guerrilla fighters and started a revolutionary war against government forces.
By 1958, the revolution had spread throughout Cuba, culminating in the fall of Havana in early 1959. Batista fled the country in 1959 and Castro formed a liberal nationalist government. He wanted Cuba to be free from US influence.
Castro wanted to remove the stranglehold that US business had on the economy. US businesses were nationalised and land reform limited the size of farms. This meant that the Cuban economy could begin to work for poorer Cubans instead of Americans and corrupt upper-classes.