Spanish and Portuguese missionaries visited from the 16th century, and Cambodia became a protectorate of France in the 19th century, being ruled as part of French Indochina. Cambodia became an independent kingdom in 1953 under Norodom Sihanouk. The Vietnam War extended into Cambodia, giving rise to the Khmer Rouge, which took Phnom Penh in 1975 and carried out a campaign of mass killing. Following an invasion by Vietnam, the Khmer Rouge were deposed and the People's Republic of Kampuchea was established. After years of isolation, the war-ravaged nation was reunited under the monarchy in 1993 and has seen rapid economic progress while rebuilding