Question: what is the difference between north vietnamese army and viet cong?
Answer: As explained in the responses here, the North Vietnamese (NVA or PAVN) were the formal army of North Vietnam while the Viet Cong (short for Vietnamese Communist) was the guerrilla Army of South Vietnam. Actually, the Viet Cong was formed from the remnants of the Viet Minh who had successful fought the French.