foco

thumb|310px|Raul Castro|Raúl Castro (left) and [[Che Guevara (right) in their Sierra de Cristal Mountain stronghold south of Havana, in 1958. It was during this time as a guerrilla commander in the Cuban Revolution, that Guevara would base his theory of a foco-centered revolution.]]

A guerrilla foco is a small cadre of revolutionaries operating in a nation's countryside. This guerrilla organization was popularized by Che Guevara in his book Guerrilla Warfare, which was based on his experiences in the Cuban Revolution. Guevara would go on to argue that a foco was politically necessary for the success of a socialist revolution. Originally Guevara theorized that a foco was only useful in overthrowing personalistic military dictatorships and not liberal democratic capitalism where a peaceful overthrow was believed possible. Years later, Guevara would revise his thesis and argue all nations in Latin America, including liberal democracies, could be overthrown by a guerrilla foco. Eventually the foco thesis would be that political conditions would not even need to be ripe for revolutions to be successful, since the sheer existence of a guerrilla foco would create ripe conditions by itself. Guevara's theory of foco, known as foquismo (), was self-described as the application of Marxism-Leninism to Latin American conditions, and would later be further popularized by author Régis Debray. The proposed necessity of a guerrilla foco proved influential in Latin America, but was also heavily criticized by other socialists.