A change in the Cambodian government allowed a window of opportunity for the destruction of the base areas in 1970 when Prince Norodom Sihanouk was deposed and replaced by pro-American General Lon Nol. The pro-American Lon Nol demanded the Vietcong forces to leave Cambodia, they refused and took control of much of the East and North of Cambodia. Lon Nol and the South Vietnamese responded by launching an invasion of the border region and forcing the anti government fighters to leave the area to safer Vietnamese controlled Kratie provinces to the north. Some elements of the anti government forces including the PRG left the area while under pressure from Cambodian and South Vietnamese forces. This operation was seen as a precursor to the much larger Cambodian Campaign a month later.