foreign policy was strongly anti-imperialist, believing that every nation should control its own natural resources. He supported Che Guevara's "Andean project", an unsuccessful plan to set up a guerrilla movement in the highlands of Bolivia, Peru and Argentina. He allowed revolutionary groups from around the world, from the Viet Cong to the Black Panthers, to train in Cuba. He considered Western-dominated Africa to be ripe for revolution, and sent troops and medics to aid Ahmed Ben Bella's socialist regime in Algeria during the Sand War. He also allied with Alphonse Massamba-Débat's socialist government in Congo-Brazzaville. In 1965, Castro authorized Che Guevara to travel to Congo-Kinshasa to train revolutionaries against the Western-backed government. Castro was personally devastated when Guevara was killed by CIA-backed troops in Bolivia in October 1967 and publicly attributed it to Guevara's disregard for his own safety. In 1966, Castro staged a Tri-Continental Conference of Africa, Asia and Latin America in Havana, further establishing himself as a significant player on the world stage. From this conference, Castro created the Latin American Solidarity Organization (OLAS), which adopted the slogan of "The duty of a revolution is to make revolution", signifying Havana's leadership of Latin America's revolutionary movement. Castro's increasing role on the world stage strained his relationship with the USSR, now under the leadership of Leonid Brezhnev. Asserting Cuba's independence, Castro refused to sign the Treaty on the Non-Proliferation of Nuclear Weapons, declaring it a Soviet-US attempt to dominate the Third World. Diverting from Soviet Marxist doctrine, he suggested that Cuban society could evolve straight to pure communism rather than gradually progress through various stages of socialism. In turn, the Soviet-loyalist Aníbal Escalante began organizing a government network of opposition to Castro, though in January 1968, he and his supporters were arrested for allegedly passing state secrets to Moscow. Recognising Cuba's economic dependence on the Soviets, Castro relented to Brezhnev's pressure to be obedient, and in August 1968 he denounced the leaders of the Prague Spring and praised the Warsaw Pact invasion of Czechoslovakia. Influenced by China's Great Leap Forward, in 1968 Castro proclaimed a Great Revolutionary Offensive, closing all remaining privately owned shops and businesses and denouncing their owners as capitalist counter-revolutionaries. The severe lack of consumer goods for purchase led productivity to decline, as large sectors of the population felt little incentive to work hard. This was exacerbated by the perception that a revolutionary elite had emerged,