Initially, communist North Vietnam was a strong ally of the Khmer Rouge while it was fighting against Lon Nol's Khmer Republic during the 1970–1975 civil war. Only after the Khmer Rouge took power things began to turn sour, when on 1 May 1975 (the day after Saigon fell), Khmer Rouge soldiers raided the islands of Phu Quoc and Tho Chau, killing more than five hundred Vietnamese civilians; following the attack, the islands were swiftly recaptured by Hanoi. Even then, the first reactions of the Vietnamese were ambiguous, and it took Vietnam a long time to react with force, for the first impulse was to arrange matters "within the family sphere".