What country did the Vietcong do most of their fighting?

South Vietnam was the turf of the Viet Cong (VC). NVA moved through Laos & Cambodia via the Ho Chi Minh Trail. Although, the VC could use sanctuaries in Cambodia (COSVN-Central Office South Vietnam; which we went after, under Nixon's Cambodian Invasion (Incursion) on 01 May 1970-resulting in the Kent State University Shooting on 04 May 1970).