Vietnamization was a policy of the Richard Nixon administration to end U.S. involvement in the Vietnam War through a program to "expand, equip, and train South Vietnam's forces and assign to them an ever-increasing combat role, at the same time steadily reducing the number of U.S. combat troops." Brought on by the Viet Cong's Tet Offensive, the policy referred to U.S. combat troops specifically in the ground combat role, but did not reject combat by the U.S. Air Force, as well as the support to South Vietnam, consistent with the policies of U.S. foreign military assistance organizations. U.S. citizens' mistrust of their government that had begun after the offensive worsened with the release of news about U.S. soldiers massacring civilians at My Lai (1968), the invasion of Cambodia (1970), and the leaking of the Pentagon Papers (1971).