To resist the Vietnamese occupation of Kampuchea and the government which they installed, the Khmer Rouge called on the Kampuchean people to unite and fight the Vietnamese. However, due to the brutality which they had experienced under the deposed government, many Kampucheans believed that any political movement aimed at restoring national freedom must oppose both the Khmer Rouge and the Vietnamese. In response to such preconditions, two non-communist movements were formed to fight the Vietnamese occupation. The first group, a right-wing and pro-Western organisation, was formed in October 1979 by former Prime Minister Son Sann and was called the Khmer People's National Liberation Front (KPNLF). The KPNLF operated from several refugee camps on the Thai-Cambodian border, where it controlled thousands of civilians. At its peak, the armed branch of the KPNLF were estimated to have between 12,000 and 15,000 fighters, but a third of that number were lost through fighting and desertions during the Vietnamese dry season offensive of 1984–1985. Nonetheless, the KPNLF continued to operate in small groups, harassing the Vietnamese and their Kampuchean allies using guerrilla tactics.