Vietnam was as much a modern war than an insurgency. The Chinese/Soviet govts supplied the PAVN with modern weapons including air defence, armour, and an air force. The Viet Cong were the irregular militia forces that supplemented that. At least by the time of US deployment.

Though then again, that started with a unit of 23 people equipped with a machine gun and two revolvers. It really doesn’t take long for any militia to achieve some serious weaponry if it can get the attention of sympathetic states.