Fidel and Raul Castro formed an underground movement in the early 1950s to overthrow the brutal and corrupt regime of the dictator Fulgencio Batista, under whose rule Cuba had become a haven for organized crime.
After an unsuccessful rising against Batista in 1953 the Castro brothers were jailed for 15 years, but were released after two years and exiled to Mexico where they met the charismatic Argentinian doctor Ernesto ‘Che’ Guevara.
Returning to Cuba with Guevara and a small band of followers in 1956, they joined with mountain bandits. From their stronghold in Sierra Maestra they smuggled arms, mounted guerrilla raids, blew up bridges, kidnapped Americans and cut off the ports from which sugar was exported.
Batista finally fled on New Year’s Eve 1958, and Fidel Castro, at the age of 30, entered Havana in triumph on 8 January 1959.
Source: history.blog.gov. uk