Original sentence: The nickname "Charlie" used by US servicemen in the Vietnam War is derived from "Victor Charlie", the NATO phoneticism of the initials of Viet Cong, the armed insurgents in the Republic of Vietnam (South Vietnam)
Edited sentence: The nickname "Charlie" used by US servicemen in the Vietnam War is derived from "Victor Charlie", the NATO phoneticism of the initials of Viet Cong, a derogatory name referring to the armed insurgents in the Republic of Vietnam (South Vietnam)