on Cuba on March 14, 1958, during the armed conflict of 1953-1958 between rebels led by Fidel Castro and the Fulgencio Batista régime. Arms sales violated U.S. policy which had permitted the sale of weapons to Latin-American countries which had signed the 1947 Inter-American Treaty of Reciprocal Assistance (Rio Treaty) as long as the weapons were not used for hostile purposes. The arms embargo had more of an impact on Batista than on the rebels. After the Castro socialist government came to power on January 1, 1959, relations were initially friendly between Castro and the Dwight D. Eisenhower administration but became strained after the Agricultural Reform confiscated land owned by many American businesses and Cuba continued to sponsor revolutionary movements in other parts of the Caribbean. By March 1960 the US government began making plans to help overthrow the Castro administration. Congress did not want to lift the embargo. In April 1960, the US Department of State issued a memorandum from Deputy Assistant Secretary of State for Inter-American Affairs Lester D. Mallory to his immediate superior, Roy Rubottom, acknowledging majority support within Cuba for the Castro administration, the fast spread of communism within the country, and the lack of an effective political opposition. The memorandum stated that the "only foreseeable means of alienating internal support is through disenchantment and disaffection based on economic dissatisfaction and hardship." It recommended a policy that would be "adroit and inconspicuous as possible" while aiming to deny "money and supplies to Cuba, to decrease monetary and real wages, to bring about hunger, desperation and overthrow of government." In May 1960 the Cuban government began regularly and openly purchasing armaments from the Soviet Union, citing the US arms embargo. In July 1960 the United States reduced the import quota of brown sugar from Cuba to 700,000 tons under the Sugar Act of 1948; and the Soviet Union responded by agreeing to purchase the sugar instead. In June 1960 a key incident occurred: Eisenhower's government refused to export oil to the island, leaving Cuba reliant on Soviet crude oil, which the American companies in Cuba refused to refine. This led the Cuban government to nationalize all three American-owned oil refineries in Cuba in response. The refinery owners were not compensated for the nationalization of their property. The refineries became part of the state-run company, Unión Cuba-Petróleo. This prompted the Eisenhower administration to launch the first trade embargo—a