Complex sentence: It survived as a clandestine organization under the leadership of Ibrahim Abatcha, until it merged itself in 1966 with the General Union of the Children of Chad to form the National Liberation Front of Chad (FROLINAT).
Split into simpler sentences: It survived as a clandestine organization under the leadership of Ibrahim Abatcha. In 1966 the party merged with the General Union of the Children of Chad to form the National Liberation Front of Chad (FROLINAT).