This presence was initially tolerated by Prince Sihanouk, the Cambodian head of state, but domestic resistance combined with China and North Vietnam aiding the anti-government Khmer Rouge caused him to request help from the Soviet Union to stop this.

The U.S. assisted the Khmer government with massive U.S. aerial bombing campaigns and direct material and financial aid, while the PAVN continued to occupy Cambodian territory and occasionally engage the FANK in combat.

[14] Neither the People's Republic of China (PRC) nor North Vietnam disputed Sihanouk's claim to represent "progressive" political policies and the leadership of the prince's domestic leftist opposition, the Pracheachon Party, had been integrated into the government.

"[16] During the same year, however, he allowed his pro-American minister of defense, General Lon Nol, to crack down on leftist activities, crushing the Pracheachon by accusing its members of subversion and subservience to Hanoi.

[18] Simultaneously, Sihanouk lost the support of Cambodia's conservatives as a result of his failure to come to grips with the deteriorating economic situation (exacerbated by the loss of rice exports, most of which went to the PAVN/Viet Cong) and with the growing communist military presence.

[19][20] Lon Nol was chosen by the right as prime minister and, as his deputy, they named Prince Sirik Matak; an ultraconservative member of the Sisowath branch of the royal clan and long-time enemy of Sihanouk.

In addition to these developments and the clash of interests among Phnom Penh's politicized elite, social tensions created a favorable environment for the growth of a domestic communist insurgency in the rural areas.

To maintain the balance against the rising tide of the conservatives, he named the leaders of the very group he had been oppressing as members of a "counter-government" that was meant to monitor and criticize Lon Nol's administration.

[26] After returning home in March, Sihanouk abandoned his centrist position and personally ordered the arrest of Khieu Samphan, Hou Yuon, and Hu Nim, the leaders of the "counter government", all of whom escaped into the northeast.

The prince's decimation of the Prachea Chon and the urban communists had, however, cleared the field of competition for Saloth Sar (also known as Pol Pot), Ieng Sary, and Son Sen—the Maoist leadership of the maquisards.

[36] Although the U.S. had been aware of the PAVN/Viet Cong sanctuaries in Cambodia since 1966, President Lyndon B. Johnson had chosen not to attack them due to possible international repercussions and his belief that Sihanouk could be convinced to alter his policies.

[37] Johnson did, however, authorize the reconnaissance teams of the highly classified Military Assistance Command, Vietnam Studies and Observations Group (SOG) to enter Cambodia and gather intelligence on the Base Areas in 1967.

[citation needed] On 18 March 1969, on secret orders from Nixon and Henry Kissinger, the U.S. Air Force carried out the bombing of Base Area 353 (in the Fishhook region opposite South Vietnam's Tây Ninh Province) by 59 B-52 Stratofortress bombers.

[41] Sihanouk told U.S. diplomat Chester Bowles on 10 January 1968, that he would not oppose American "hot pursuit" of retreating North Vietnamese troops "in remote areas [of Cambodia]," provided that Cambodians were unharmed.

[47] This view has been disputed,[48][49][50] with documents uncovered from the Soviet archives revealing that the North Vietnamese offensive in Cambodia in 1970 was launched at the explicit request of the Khmer Rouge following negotiations with Nuon Chea.

[54] While Sihanouk was out of the country on a trip to France, anti-Vietnamese rioting (which was semi-sponsored by the government) took place in Phnom Penh, during which the North Vietnamese and Viet Cong embassies were sacked.

"[63] The North Vietnamese reacted to the political changes in Cambodia by sending Premier Phạm Văn Đồng to meet Sihanouk in China and recruit him into an alliance with the Khmer Rouge.

[citation needed] The prince then allied himself with the Khmer Rouge, the North Vietnamese, the Laotian Pathet Lao and the Viet Cong, throwing his personal prestige behind the communists.

Having realized that such a front would exclude the Soviet Union and implicitly challenge the hegemonic role that the DRV had arrogated to itself in Indochina, the North Vietnamese leaders declared that all communist states should join forces against "American imperialism.

[80] One month prior, the North Vietnamese had launched an offensive (Campaign X) of its own against FANK forces at the request of the Khmer Rouge[81] and in order to protect and expand their Base Areas and logistical system.

FANK, whose ranks had been increased by thousands of young urban Cambodians who had flocked to join it in the months following the removal of Sihanouk, had expanded well beyond its capacity to absorb the new men.

Khmer Rouge forces, which had been reorganized at an Indochinese summit held in Guangzhou, China in April 1970, would grow from 12 to 15,000 in 1970 to 35–40,000 by 1972, when the so-called "Khmerization" of the conflict took place and combat operations against the Republic were handed over completely to the insurgents.

[106] By late 1973, there was a growing awareness among the government and population of Cambodia that the extremism, total lack of concern over casualties, and complete rejection of any offer of peace talks "began to suggest that Khmer Rouge fanaticism and capacity for violence were deeper than anyone had suspected.

There were tales of the forced relocations of entire villages, of the summary execution of any who disobeyed or even asked questions, the forbidding of religious practices, of monks who were defrocked or murdered, and where traditional sexual and marital habits were foresworn.

During 1973, the communist party fell under the control of its most fanatical members, Pol Pot and Son Sen, who believed that "Cambodia was to go through a total social revolution and that everything that had preceded it was anathema and must be destroyed.

The economy had been gutted, the transportation network had been reduced to air and waterways, the rice harvest had fallen by one-quarter, and the supply of freshwater fish (the chief source of protein for the country) had declined drastically.

The situation was best described by General Sak Sutsakhan (now FANK chief of staff): The picture of the Khmer Republic which came to mind at that time was one of a sick man who survived only by outside means and that, in its condition, the administration of medication, however efficient it might be, was probably of no further value.

Ambassador John Gunther Dean, other American diplomatic personnel, Acting President Saukam Khoy, senior Khmer Republic government officials and their families, and members of the news media.

[129]: 192–3  Khmer Rouge troops immediately began to forcibly empty the capital city, driving the population into the countryside and killing tens of thousands of civilians in the process.

[135] The Khmer Rouge forcibly evacuated the entire city after taking it, in what has been described as a death march: François Ponchaud wrote: "I shall never forget one cripple who had neither hands nor feet, writhing along the ground like a severed worm, or a weeping father carrying his ten-year-old daughter wrapped in a sheet tied around his neck like a sling, or the man with his foot dangling at the end of a leg to which it was attached by nothing but skin";[136] John Swain recalled that the Khmer Rouge were "tipping out patients from the hospitals like garbage into the streets ...