 Complete the following phrase:  In 1968, the Viet Cong launched a massive and surprise Tết Offensive known in South Vietnam as Biến Cố Tết Mậu Thân or in the North as Cuộc Tổng Tấn Công và Nổi Dậy Tết Mậu Thân, attacking almost all major cities in South Vietnam over the Vietnamese New Year Tết. The Viet Cong and North Vietnamese captured the city of 