The United States continued its unilateral withdrawal of forces from South Vietnam notwithstanding the lack of progress at the Paris Peace Talks. The removal of Prince Norodom Sihanouk from power in Cambodia in March and his replacement by General Lon Nol, began the Cambodian Civil War. South Vietnamese and U.S. forces entered Cambodia in late April to attack People's Army of Vietnam (PAVN) and Vietcong (VC) bases and supply lines there which had long been used to support the insurgency in South Vietnam. The expansion of the war revitalized the antiwar movement in the U.S. and led to the Kent State shootings and Jackson State killings in May. While U.S. ground forces withdrew from Cambodia at the end of June and legislation was passed to prevent their reintroduction, the South Vietnamese c