Although the PAVN lost militarily to the US forces and ARVN in the south, the political impact of the war in the United States was strong. Public demonstrations increased in ferocity and quantity after the Tet Offensive. During 1970, the 5th, 7th and 9th Divisions fought in Cambodia against U.S., ARVN, and Cambodian Khmer National Armed Forces but they had gained new allies: the Khmer Rouge and guerrilla fighters supporting deposed Prime Minister Sihanouk. In 1975 the PAVN were successful in aiding the Khmer Rouge in toppling Lon Nol's U.S.-backed regime, despite heavy US bombing. After the withdrawal of most U.S. combat forces from Indochina because of the Vietnamization strategy, the PAVN launched the ill-fated Easter Offensive in 1972. Although successful at the beginning, the South Vietnamese repulsed the main assaults with U.S. air support. Still North Vietnam retained some South Vietnamese territory. Nearly two years after the full U.S. withdrawal from Indochina in accordance with the terms of the 1973 Paris Peace Accords, the PAVN launched a Spring Offensive aimed at overthrowing the South Vietnamese government and uniting Vietnam under communist rule. Without direct support of the U.S., and suffering from stresses caused by dwindling aid, the ARVN was ill-prepared to confront the highly motivated PAVN, and despite the on paper superiority of the ARVN, the PAVN quickly secured victory within two months and captured Saigon on 30 April 1975, ending the 20 year Vietnam war. After national reunification, the LASV was officially merged into PAVN on 2 July 1976. Sino-Vietnamese conflicts (1975–1990) Towards the second half of the 20th century the armed forces of Vietnam would participate in organised incursions to protect its citizens and allies against aggressive military factions in the neighbouring Indochinese countries of Laos and Cambodia, and the defensive border wars with China. The PAVN had forces in Laos to secure the Ho Chi Minh Trail and to militarily support the Pathet Lao. In 1975 the Pathet Lao and PAVN forces succeeded in toppling the Royal Laotian regime and installing a new, and pro-Hanoi government, the Lao People's Democratic Republic, that rules Laos to this day. Parts of Sihanouk's neutral Cambodia were occupied by troops as well. A pro US coup led by Lon Nol in 1970 led to the foundation pro-US Khmer Republic state. This marked the beginning of the Cambodian Civil War. The PAVN aided Khmer Rouge forces in toppling Lon Nol's government