What political change did fidel castro undergo after taking power?

When Fidel Castro was elected Prime Minister of Cuba and took power in 1959, Castro announced that he - and his administration - were communists and that they welcomed support and aid from the communist Soviet Union. While other Western powers were aware of Castro's socialistic leanings, his willingness to announce himself as a communist, and encourage support from the Soviet Union was a surprise to many Cuban citizens and, also, other Western nations, particularly the United States.