Now the United States feared the domino theory had come into play in Southeast Asia. The signs were all there: soon after China's 1947 communist revolution they began to support Ho Chi Minh's nationalist ambitions in Vietnam. Though many observers saw Ho as being a nationalist first and a communist second, China's overtures made it all the more easy for him to espouse communism as the answer to the national struggle. China's conversion to communism was scary enough for US officials - the thought of Vietnam following suit inspired an ugly premonition: if a united Vietnam became communist, Laos and Cambodia would fall with it; other Southeast Asian nations from Thailand to Indonesia would become even more vulnerable. Worse-case scenarios of a communist India or Australia fell into place quite easily thanks to the logic of domino theory. As far as the United States was concerned, South Vietnam would become the bulwark for Western capitalism and democracy; Ho Chi Minh's aspirations for a united communist Vietnam would not be tolerated.

In the grand scheme of Asian domino theory, the former Indochina colonies - including Cambodia - were considered a collective domino waiting to topple; understandably, Sihanouk's subsequent public courtship with communist leaders angered many American politicians. Unfortunately neither the US nor Sihanouk himself was very successful at burying the hatchet, so political tensions would rise on a reoccurring basis. For example, Sihanouk often complained that US officials would treat him like a child during private diplomatic meetings, chastising him on how he ran his affairs. Sihanouk would then respond in kind with bombastic anti-US rhetoric that would infuriate the Americans. And in 1959, when Sihanouk successfully quashed an anti-royalist uprising in Siem Reap province, he blamed the entire incident on a CIA-supported attempt to overthrow him. Yet despite the tempestuousness of their relationship, the US managed to support Cambodia with financial aid. These funds built up Cambodian infrastructure and encouraged Sihanouk to stick with Washington's agenda. Some of his ministers, including a frail but well-connected general named Lon Nol, became friendly with the US thanks to the steady flow of economic aid.

In 1963, unpopular South Vietnamese president Ngo Dinh Diem was murdered in a coup that was tacitly supported by the US. Sihanouk was furious with what he saw as the United States' arrogant interference in Asia's local affairs, so he refused further aid and ordered the US embassy staff out of Cambodia. In numerous public diatribes he levied charges that the US was still supporting Son Ngoc Thanh, the once-popular anti-monarchist partisan whom he personally despised. Privately, Lon Nol and other pro-US ministers were uncomfortable with Sihanouk's turn against the US, yet they knew they were in no position to do much about it. And in what may have been an attempt to send positive signals to China and North Vietnam, Sihanouk announced he would nationalize much of the country's industrial infrastructure, declaring himself an ardent socialist and a crusader against Western imperialism.

Meanwhile a new war between North and South Vietnam escalated. The French were long gone from the scene, so American presidents Kennedy and Johnson successively supplied a growing stream of military advisors to aid South Vietnam's Army of the Republic of Vietnam (ARVN). ARVN, a poorly commanded and often corrupt fighting force, was up against two deadly foes: the North Vietnam Army (NVA), the North's regular army, and the Viet Cong (VC), an intricate guerrilla network of armed South Vietnamese citizens who supported Hanoi's fight for reunification with the South.

As early as 1965, Prince Sihanouk quietly tolerated small VC/NVA camps inside the Cambodian border. Because Cambodia was internationally regarded as neutral, both North and South Vietnam were supposed to respect its borders. But the communists gambled that they could take advantage of Sihanouk's military weakness and hide in Cambodian forests along the border. If the United States ever discovered the intrusion, the communists bet that President Johnson wouldn't have the stomach for a fight in a neutral, noncombatant country (though it should be noted that the US had no such aversion to engaging in a secret war in neutral Laos, where North Vietnamese troop movements were more flagrant). Sihanouk knew he couldn't afford to make Hanoi an enemy, so he never raised a significant protest against these border incursions. Similarly, China forced him to open up his southern port city of Sihanoukville to clandestine supply smuggling to the Viet Cong, whose previous smuggling route along the Ho Chi Minh Trail through Laos had been hampered by covert US bombing. Again, Sihanouk did not protest, despite his private distaste for the communists. At least in the case of the Sihanoukville smuggling operation there was serious money to be made, so in order to placate his pro-US ministers, Sihanouk allowed them to take a piece of the concessions. These illicit profits gave these ministers and the Cambodian armed forces an early taste of the rampant corruption that would later erode military discipline to the breaking point.

As US intelligence received reports of communist supply movements within Cambodian territory, the CIA began to recruit Vietnamese of ethnic Cambodian descent - the Khmer Krom - to infiltrate the border and stop the flow of shipments. The CIA often brought in Son Ngoc Thanh, himself a Krom, to recruit volunteers. These search-and-destroy missions, as fate would have it, were not very successful; in fact, they may have encouraged more VC and NVA units to cross into Cambodia to protect their operations. American military officials became more and more fed up with Cambodia's growing infection. US General William Westmoreland encouraged decisive action, including a full-scale invasion of Cambodia, but President Johnson refused, for he was convinced he could turn Sihanouk towards complete cooperation with the US without bringing Cambodia into the war.

As the war increased in Vietnam and Laos, Sihanouk's politics started to swing to the right. More and more members of the Sangkum were anti-Sihanouk conservatives, which forced the prince to work with them in order to maintain power. In 1966 he appointed a more conservative government and he ordered Lon Nol to crush a leftist uprising in Battambang province, which he did with ruthless success. The violence of the uprising was the final straw for many of the remaining left-wing politicians, including Khieu Samphan. Khieu and other leftists joined their colleagues in the wilderness, who had fled for their safety several years earlier. For many years, though, Khieu Samphan was believed to be dead, a victim of a bloody Sihanouk purge.

Increased US operations in 1967 forced more NVA over the Cambodian border. Sihanouk was becoming more nervous every day, worried by both this troop escalation and the growing violence emanating from the Cultural Revolution in China. Concluding he had little alternative, Sihanouk again began to make overtures to the US. It was classic Sihanouk as he managed to lecture US officials about their involvement in Vietnam while asking to do business with them if they would recognize Cambodia's borders. Soon enough the money began to flow, and President Johnson promised the US would recognized Cambodia's neutrality and integrity. This policy would remain in place until the inauguration of President Richard Nixon in January 1969.

Next: Nixon's War: The Bombings