Cuba and Venezuela established relations in 1902. In 1999, the bilateral trade and military relationship significantly improved during the presidency of Hugo Chávez as Chávez allied with Cuban President Fidel Castro.
Cuba and Russia are longtime allies of Venezuela and its socialist government. Russia has supplied economic support and military equipment to the government of Nicolás Maduro, while Venezuela has sent oil subsidies worth billions of dollars to Cuba in exchange for medical aid and intelligence advisors.
As Interim President Juan Guaidó tries to ignite the military to support the constitution of Venezuela, the presence of Cuban troops in the country makes this more difficult.
In an interview with the Washington Post, former Venezuelan Army Lieutenant Colonel Carlos Jose Montiel Lopez, who escaped to the United States in 2018, said Cubans dressed in civilian clothing acted as "our supervisors and decision-makers."
U.S. National Security Adviser John Bolton said at the White House: "I think it's fear of the 20,000 to 25,000 Cuban security forces in the country" that prevented Venezuelan troops from heeding Guaidó's call. Bolton further stated that "If this afternoon 20-25,000 Cubans left Venezuela, I think Maduro would fall by midnight. It's this foreign presence that sits on top of the military, sits on top of the government, that makes it impossible for the people's voice to be heard."
Carlos Fernández de Cossío, Cuba’s chief of U.S. Affairs, told the Associated Press that "the 20,000 Cubans in Venezuela are primarily medical workers. Cuba does not participate in military operations nor in security operations in Venezuela." Fernández, however, noted that as hemispheric partners Cuba and Venezuela have the sovereign right to military and intelligence cooperation.
Contrary to Fernández’s remarks, in an article the New York Times published on March 17, 2019, several Cuban doctors sent to Venezuela by the Cuban government described how their Cuban and Venezuelan superiors ordered them to use medical assistance as a political weapon. Carlos Ramirez, a doctor who defected to Ecuador after six years, told the New York Times: “You arrived with vitamins and some pills for blood pressure. And when you started to gain their trust, you started the questions: ‘Do you know where your voting place is? Are you going to vote?’”
In a Washington Post article, Fernando Cutz, who was a senior adviser to then-National Security Adviser H.R. McMaster, and served as South America director in the National Security Council, said: "There is no doubt that Cubans are very much assisting the Venezuelan regime — the Maduro regime — to stay in power."
Venezuelan General Antonio Rivero, exiled in the United States, said in a 2010 interview with Spanish daily La Vanguardia, that “the penetration of Cuban officers into the Venezuelan armed forces is to monitor and supervise the military doctrinal elements at the command and staff levels.” In an interview with El Nuevo Herald in January 2015, he estimated that figure "to be 20,000 Cuban fighters who could come out in defense of the Bolivarian Revolution in case of a military uprising against Chavismo."