Since the Tongan language was not written down until the 19th century, the early history of Tonga (which means "south") is based on oral tradition. Hereditary absolute kings (Tu'i Tonga) date back to Ahoeitu in the 10th century. Around the 14th century, the twenty-third king, Kau'ulufonua, while retaining his sacred powers, divested himself of much of his executive authority, transferring it to his brother Ma'ungamotu'a, whom he thereafter called the Tu'i Ha'atakalaua. About the middle of the 17th century, the seventh temporal king, Fotofili, transferred the executive power to his brother Ngala, called the Tu'i Kanokupolu, and thereafter the powers gradually passed into the hands of the latter and his descendants. According to tradition, in the mid-19th century, upon the death of the then Tu'i Tonga, those powers were conferred upon the nineteenth Tu'i Kanokupolu, Taufa'ahu Tupou, founder of the present dynasty.
European chronicles disclose that the island of Niuatoputapu was discovered by the Dutch navigators Jan Schouten and Jacob le Maire in 1616. In 1643, Abel Tasman discovered Tongatapu, and from then until 1767, when Samuel Wallis anchored at Niuatoputapu, there was no contact with the outside world. Capt. James Cook visited the Tongatapu and Ha'apai groups in 1773 and again in 1777, and called Lifuka in the Ha'apai group the "friendly island" because of the gentle nature of its people— hence the archipelago received its nickname, the Friendly Islands. It was in the waters of the Ha'apai group that the famous mutiny on the British ship Bounty occurred in 1789. The first Wesleyan missionaries landed in Tonga in 1826.
The first half of the 19th century was a period of civil conflict in Tonga, as three lines of kings all sought dominance. They were finally checked during the reign of Taufa'ahu Tupou, who in 1831 took the name George. By conquest, George Tupou I (r.1845–93) gathered all power in his own hands and united the islands; he abolished the feudal system of land tenure and became a constitutional monarch in 1875. Meanwhile, by the middle of the century, most Tongans had become Christians, the great majority being Wesleyans, and the king himself was strongly influenced by the missionaries.
In the latter part of the century, there were religious and civil conflicts between the Wesleyan Mission Church and the newly established Free Wesleyan Church of Tonga. After the dismissal of the prime minister, the Rev. Shirley Waldemar Baker, in 1890, the new government allowed full freedom of worship. Ten years later, during the reign (1893–1918) of George II, a treaty of friendship was concluded between the United Kingdom and Tonga, and a protectorate was proclaimed. During World War II, Tongan soldiers under Allied command fought the Japanese in the Solomon Islands, and New Zealand and US forces were stationed on Tongatapu, which served as an important shipping point.
Two more treaties of friendship between the United Kingdom and Tonga were signed in 1958 and 1968, according to which Tonga remained under British protection, but with full freedom in internal affairs. On 4 June 1970, Tonga ceased being a British protectorate and became an independent member of the Commonwealth of Nations, with King Taufa'ahau Tupou IV— who had succeeded to the throne upon the death of his mother, Queen Salote Tupou (r.1918–65)—as head of state. The new status brought few immediate changes, apart from the fact that it added Tongan control of foreign affairs to self-rule in domestic matters.
In 1972, Tonga claimed the uninhabited Minerva Reefs (now Teleki Tokelau and Teleki Tonga), situated about 480 km (300 mi) southwest of Nuku'alofa, in order to prevent an Anglo-American corporation from founding an independent Republic of Minerva on the reefs in order to gain certain tax advantages. The nation in 1973 celebrated the bicentennial of Cook's first visit by inaugurating the new runway for jet aircraft at the main airport, near Nuku'alofa. The worst tropical storm in Tonga's history, Cyclone Isaac, devastated the islands in March 1982.
Many of the government's strongest critics gained seats in the 1987 legislative elections; the unprecedented turnover was thought to reflect changing attitudes toward traditional authority. However, the traditional leaders continued in charge of the government, with Prince Fatafehi Tu'ipelehake elected as prime minister. The island's dissident pro-democracy movement, led by Akilisi Pohive, won the February 1990 general election, but it remained a minority within the legislature. A government scandal over selling Tongan passports to Hong Kong Chinese led to popular support for the opposition. Baron Vaea replaced Prince Fatafehi Tu'ipelehake as prime minister in August 1991. King Taufa'ahau Tupou IV organized the Christian Democratic Party in time for the 1993 election to provide greater coordination for his supporters and to weaken the democracy movement. However, pressure from the pro-democracy forces continued in the February 1993 general election when the People's Democratic Movement won six of the nine seats open.
Parliamentary elections were held in March 1999, when about 51% of eligible voters cast ballots, the lowest voter turnout in the country's history. Five of the nine members elected were from the Human Rights and Democracy Movement (HRDM). King Taufa'ahu Tupou IV appointed his youngest son, 41-year-old Prince Lavaka Ata Ulukalala prime minister in January 2000. When the previous prime minister retired, observers speculated that the king's oldest son, Crown Prince Tupouto'a, would be named prime minister. It is likely that Tupouto'a was passed over for the post because of his stated opposition to preserving the king's right to make lifetime appointments. His younger brother, who became the country's fourth prime minister since 1950, has been outspoken in his criticism of the country's democracy movement.
Fifty-two candidates ran for the nine people's representative seats in the legislature in March 2002; the HRDM won seven of the seats. Although the movement's improvement in electoral standing may signal popular support for democratic reform, it is seen as the king's prerogative to initiate change.
Tonga experienced a financial scandal in 2001, when the king's official court jester, an American businessman, invested $26 million in a government trust fund that subsequently disappeared. The money had been raised by the sale of Tongan citizenship and special passports to Asians, especially Hong Kong Chinese concerned with the transfer of Hong Kong to China. The $26 million represented more than half the government's annual budget.