This is a bit complicated:
Cuba was under Fulgencio Batista's reign by the time of Castro's rise. Cuba was a capitalist country at that point that was basically the US' puppet. Fidel Castro and his "guerrillas" were obviously against the system that was being employed for many reasons. I believe one of the main reasons was that Batista's Cuba was a corrupt one. There were many under-the-books assassinations just because they were a threat to Batista, etc. Overall, Cuba was a very corrupt and injust country at that point and that is why Fidel decided to fight against it, beginning with the "27 de julio movement" alongside Ernesto "Ché" Guevara.
