 On 18 March , the Cambodian National Assembly deposed Sihanouk and named Lon Nol as provisional head of state . This led Sihanouk to immediately establish a government @-@ in @-@ exile in Beijing and to ally himself with North Vietnam , the Khmer Rouge , the NLF , and the <unk> <unk> Lao . In doing so , Sihanouk lent his name and popularity in the rural areas of Cambodia to a movement over which he had little control . The North Vietnamese response to the coup was swift . PAVN began directly supplying large amounts of weapons and advisors to the Khmer Rouge , and Cambodia plunged into civil war . 
