The group was made up of people from both South and North Vietnam. Some were not communists, but the main leaders were. The Vietcong used guerilla warfare, including terrorist bombings, assassinations, and ambushes. The group is best known for the Tet Offensive, an surprise attack on many South Vietnamese cities that began on January 1968 during Tet, or Vietnamese New Year. The group was closely allied with the government of North Vietnam, which conquered the South in 1975.