The document summarizes key events and outcomes of US involvement in the Vietnam War under presidents Johnson and Nixon. It discusses escalation of bombing campaigns in Vietnam, Laos, and Cambodia, as well as domestic opposition that grew in the US. Nixon pursued a policy of "Vietnamization" to gradually withdraw US troops while training South Vietnamese forces, but the ARVN failed to prevent a North Vietnamese takeover of South Vietnam in 1975 after US withdrawal. The war had lasting negative impacts in Cambodia, where US bombing contributed to the rise of the genocidal Khmer Rouge regime.