Stephen Kinzer made this observation on Fresh Air...
Meet 'The Brothers' Who Shaped U.S. Policy, Inside And Out
by NPR Staff
October 16, 201312:33 PM
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On the Dulles' ability to overthrow regimes in Iran and Guatemala but not in Cuba or Vietnam
They were able to succeed [at regime change] in Iran and Guatemala because those were democratic societies, they were open societies. They had free press; there were all kinds of independent organizations; there were professional groups; there were labor unions; there were student groups; there were religious organizations. When you have an open society, it's very easy for covert operatives to penetrate that society and corrupt it.
Actually, one of the people who happened to be in Guatemala at the time of the coup there was the young Argentine physician Che Guevara. Later on, Che Guevara made his way to Mexico and met Fidel Castro. Castro asked him, "What happened in Guatemala?" He was fascinated; they spent long hours talking about it, and Che Guevara reported to him ... "The CIA was able to succeed because this was an open society." It was at that moment that they decided, "If we take over in Cuba, we can't allow democracy. We have to have a dictatorship. No free press, no independent organizations, because otherwise the CIA will come in and overthrow us." In fact, Castro made a speech after taking power with [Guatemalan President Jacobo] Árbenz sitting right next to him and said, "Cuba will not be like Guatemala." ...
http://www.npr.org/2013/10/16/234752747/meet-the-brothers-who-shaped-u-s-policy-inside-and-out