As early as July 1959, Castro's intelligence chief Ramiro Valdés contacted the KGB in Mexico City.[37] Subsequently, the USSR sent over one hundred mostly Spanish speaking advisors, including Enrique Líster Forján, to organize the Committees for the Defense of the Revolution.
In February 1960, Cuba signed an agreement to buy oil from the USSR. When the U.S.-owned refineries in Cuba refused to process the oil, they were expropriated, and the United States broke off diplomatic relations with the Castro government soon afterward. To the concern of the Eisenhower administration, Cuba began to establish closer ties with the Soviet Union. A variety of pacts were signed between Castro and Soviet Premier Nikita Khrushchev, allowing Cuba to receive large amounts of economic and military aid from them.
In June 1960, Eisenhower reduced Cuba's sugar import quota by 7,000,000 tons, and in response, Cuba nationalized some $850 million worth of U.S. property and businesses. The revolutionary government grabbed control of the nation by nationalizing industry, expropriating property owned by Cubans and non-Cubans alike, collectivizing agriculture, and enacting policies which would benefit the population. While popular among the poor, these policies alienated many former supporters of the revolution among the Cuban middle and upper-classes. Over one million Cubans later migrated to the U.S., forming a vocal anti-Castro community in Miami, Florida. (See Cuban-American lobby.)
President Dwight Eisenhower broke off ties on January 3, 1961, saying Fidel Castro had provoked him once too often.[38]