In the 13th century, Cambodians converted en masse to Theravada Buddhism, the variant practiced by the Khmer today. State-sponsored Hinduism, and the temples inspired by that religion, lost their importance, but for many years the kingdom remained strong and prosperous, as the Chinese emissary Zhou da guan reported in 1296. Over the next 200 years, the empire shrank, as tributary states in what is now Thailand declared their independence and invaded Cambodian territory. By 1450 or so, the capital had shifted southward to the region of present-day Phnom Penh, where it has remained ever since.
Over the next four centuries, Cambodia became a small Buddhist kingdom dependent on the goodwill of its neighbors, Thailand and Vietnam, In the mid-19th century, conflict between these kingdoms spilled onto Cambodian soil, and Cambodia almost disappeared.
In 1863 the Cambodian king, fearful of Thai intentions, asked France to provide protection for his kingdom. France kept Cambodia from being swallowed up, but the protectorate developed into a full-scale colonial relationship that the king had not foreseen.
French rule lasted until the 1950s, and was less harsh than in neighboring Vietnam. The Khmer elite was treated well and French policies had a relatively light impact on the population, while improvements in infrastructure strengthened the economy and brought Cambodia to the edges of the developed world. France's greatest contribution to Cambodia was probably its restoration of the temples at Yasodharapura. French scholars deciphered Angkorean inscriptions and rebuilt many of the temples, providing Cambodians with a glorious, precisely dated past that had been largely forgotten.
After Cambodia gained its independence from France, it entered a short period of peace and prosperity which many older Khmer now look back on as a golden age. By the late 1960s, however, Cambodia was drawn inexorably into the Vietnam War. In 1975, Communist forces, known to the outside world as Khmer Rouge or Red Khmers, overthrew the pro-American regime that had seized power five years before. In the Khmer Rouge era that followed , at least 1.2 million Cambodians died of malnutrition, overwork, executions, and mistreated diseases as the Maoist-inspired regime sought to achieve total communism overnight. Responding to Cambodian attacks, Vietnam invaded Cambodia in 1979 and established a protectorate there that lasted for 10 years.
Under peace agreements signed in Paris in 1991, Cambodia came under United Nations protection for a time in preparation for general elections that were held in 1993. Since then, Cambodia has been a constitutional monarchy ruled by a coalition government that has accepted large infusions of foreign aid. In 1999 Cambodia became a member of ASEAN, and became for the first time, after centuries of isolation, a full-fledged member of the Southeast Asian community.