On May 9, 1970, an American armored personnel carrier and its crew pass by two dead civilians staring down the side of the roadside, dead and scattered, as they enter the invasion of Cambodia during the Vietnam War.

   On May 9, 1970, an American armored personnel carrier and its crew pass by the side of two dead civilians, dead and scattered on the side of the road, as they enter the invasion of Cambodia during the Vietnam War. Cambodia was a neutral country but had long served as a sanctuary for communist forces fighting in Vietnam. South Vietnamese Army of the Republic of Vietnam (ARVN) and U.S. forces invaded Cambodia in the spring of 1970 to destroy communist stronghold areas and prevent the "North Vietnamization" of Gambodia.

On March 18, 1970, while the Vietnam War was still ongoing, Cambodian Prime Minister and Defense Minister Lon Nol staged a coup against Prince Norodom Sihanouk, who was in Paris. Ron Nol allied himself with the U.S. and demanded that the People's Army of Vietnam (PAVN, North Vietnamese Army) and the Viet Cong (VC, Vietnamese Communist Army), a communist organization in South Vietnam, withdraw from Cambodia.

  They closed the supply operations of the Democratic Republic of Vietnam (DRV, North Vietnam) from the port of Sihanoukville and closed the Ho Chi Minh route supplying the PAVN and VC forces inside South Vietnam. Lon Nol then dispatched a hopelessly weakened Cambodian army against an estimated 40,000 to 60,000 PAVN troops in the three Cambodian border provinces. The U.S. provided equipment for the Cambodian army, which had over 100,000 men, but was driven back into the cities by communist forces.

   From April 14-20, 1970, the Army of the Republic of Vietnam (ARVN, South Vietnamese Army) conducted several cross-border battalion operations to seize key communist supply depots. Vietnamese People's Army (PAVN, North Vietnamese Army) and Viet Cong (VC, Vietnamese Communist Army) units withdrew into inland Cambodia. Up to about 30 kilometers into Cambodia, about 50,000 South Vietnamese Army (ARVN) and 30,000 U.S. troops entered the war. U.S. ground forces withdrew from Cambodia by June 30. The South Vietnamese Army (ARVN) remained until 1971, creating hundreds of thousands of new Cambodian refugees. 638 South Vietnamese troops died, 338 U.S. troops died, and about 11,369 communist forces died during the invasion of Cambodia from April 29 to July 22, 1970.