<P> In January 1961, just prior to leaving office, Eisenhower formally severed relations with the Cuban government . In April 1961, the administration of newly elected American President John F. Kennedy mounted an unsuccessful CIA - organized ship - borne invasion of the island at Playa Girón and Playa Larga in Santa Clara Province--a failure that publicly humiliated the United States . Castro responded by publicly embracing Marxism--Leninism, and the Soviet Union pledged to provide further support . </P> <P> The Berlin Crisis of 1961 was the last major incident in the Cold War regarding the status of Berlin and post--World War II Germany . By the early 1950s, the Soviet approach to restricting emigration movement was emulated by most of the rest of the Eastern Bloc . However, hundreds of thousands of East Germans annually emigrated to West Germany through a "loophole" in the system that existed between East and West Berlin, where the four occupying World War II powers governed movement . </P> <P> The emigration resulted in a massive "brain drain" from East Germany to West Germany of younger educated professionals, such that nearly 20% of East Germany's population had migrated to West Germany by 1961 . That June, the Soviet Union issued a new ultimatum demanding the withdrawal of Allied forces from West Berlin . The request was rebuffed, and on 13 August, East Germany erected a barbed - wire barrier that would eventually be expanded through construction into the Berlin Wall, effectively closing the loophole . </P> <P> Continuing to seek ways to oust Castro following the Bay of Pigs Invasion, Kennedy and his administration experimented with various ways of covertly facilitating the overthrow of the Cuban government . Significant hopes were pinned on a covert program named the Cuban Project, devised under the Kennedy administration in 1961 . </P>

Who started the cold war us or soviet union