Under Prince Norodom Sihanouk and the French, a basic but rudimentary health care system was in place. During the Sihanouk and Lon Nol regimes in the 1960s and up until 1975, bombing and guerrilla warfare raged in the countryside, especially near the Cambodian-Vietnamese border. Population shifts occurred from east to west, and from rural to urban areas. During this period, the population of Phnom Penh swelled from about 25,000 to more than one million.