Complex sentence: The Savannah Association is an association of ex-servicemen of all units who were involved from 1975 to 1976 with a covert intervention by the South African Defence Force's during the Angolan War of Independence and subsequent Angolan Civil War.
Split into simpler sentences: The Savannah Association is an association of ex-servicemen of all units who were involved in the Savannah (Angola) operation. Operation Savannah was the South African Defence Force's 1975--1976 covert intervention in the Angolan War of Independence, and the subsequent Angolan Civil War.