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 Huế , after which many mass graves were found . Many of the executed victims had relations with the South Vietnamese government or the US , or part of social groups that were considered enemies to the Viet Cong , like Catholics , business owners and intellectuals ( Thảm Sát Tết Mậu Thân ) . Over the course of the year the Viet Cong forces were pushed out of all cities in South Vietnam and nearly decimated . In subsequent major offensives in later years , North Vietnamese regulars with artillery and tanks took over the fighting . In the months following the Tet Offensive , an American unit massacred civilian villagers , suspected to be sheltering Viet Cong guerillas , in the hamlet of My Lai in Central Vietnam , causing an uproar in protest around the world
My Lai
My Lai Massacre
History of Vietnam since 1945