There was quite a lot of evidence as early as 1957 that Castro had ties to the Soviet Union that exceeded simply desiring economic aid. A former Ambassado to Cuba in the late 1940's provided information suggesting Castro's true intent in an interview with a respected journal stating "... `He is a fellow-traveler, if not a member of the Communist Party and has been so for a long time. He was a ring-leader in the bloody uprising in Bogota, Colombia in April, 1948, which occurred (and obviously was planned by the Kremlin) just at the time when the Pan-American Conference was being held in that capital, with no less a person than Secretary of State George C. Marshall present. The uprising was engineered and staged by Communists, and the Colombian Government and Colombia press subsequently published documentary evidence of Fidel Castro's role as a leader in the rioting which virtually gutted the Colombian capital." This supposition has been supported by other revelations, especially since Che's death many years ago.
Eisenhower believed it was in the best interest of unity in the western hemisphere, to display anattitude of non-interference as called for in the Ninth Inter-American Conference, held in Bogota, Colombia in April 1948, which led to the creation of the Organization of American States (OAS).
Additionally, Saul Landau who was a senior fellow at the Institute for Policy Studies in Washington, DC said, following Fidel's announcement of his intent to install a Marxis-Leninist regime in 1961 "...Fidel Castro in 1968 explained to me that he had become a Marxist from the very time that he read the Communist Manifesto in his student days, (emphasis added) and a Leninist from the period when he read Lenin while in prison on the Isle of Pines in 1954."