Meanwhile a shadow war was taking place in Cambodia and Laos as American bombers tried to root out Vietnamese communist guerrillas using passage through Vietnam's neighbours. Cambodia dissolved into civil war and the Khmer Rouge seized power. The new regime, under Pol Pot, aspired to an ethnically Khmer, agrarian communist society. Large numbers of the population – an estimated 1.5 million Cambodians (20% of the population) – were killed in purges before Vietnamese forces brought an end to the Khmer Rouge's cruel and terrifying four-year reign in 1979.