U.S. troops gesture with "V" signs and clenched fists as they ride into battle near the Cambodian border on an armored personnel carrier, April 1970. President Nixon announced on April 30 that the U.S. would launch an "incursion" of Cambodia in order to disrupt Viet Cong supply lines and to destroy bases being used to support operations in South Vietnam. (AP Photo/Le Ngoc Cung)