Complex sentence: Alpha 66 is a paramilitary, anti-Fidel Castro group formed by Cuban exiles in Puerto Rico who trained during the 1960s and 1970s in the Everglades for an eventual armed invasion of Cuba.
Split into simpler sentences: Alpha 66 is a paramilitary group formed by Cuban exiles in Puerto Rico opposed to the Cuban government led by Fidel Castro. The group trained during the 1960s and 1970s in the Everglades for an eventual armed invasion of Cuba.