Tonga is a sovereign state consisting of over 169 islands and islets in the South Pacific. The kingdom covers a total of 748 square kilometres, divided into five administrative groups: The Niuas, Vava'u, Ha'apai, Tongatapu, and 'Eua. Earliest human settlement dates to the arrival of the Lapita culture around 1500 BC, from the neighbouring Polynesian islands. Between AD 950 to 1500, Tonga established itself as a pre-eminent power in the Pacific with the hegemony of the Tu'i Tonga Empire. First European contact was made with the Dutch explorers Willem Schouten and Jacob Le Maire in 1616, and Abel Tasman in 1643. Tonga was known as the Friendly Islands, following a visit by British captain James Cook in 1773, and who returned to the islands in 1774 and 1777. Tongan king George Tupou I established a European-styled constitutional monarchy in 1875, which gave Tonga a stable government. Following a Treaty of Friendship with the British in 1900, Tonga became a protected state, maintaining its sovereignty in a unique relationship until 1970 when the protectorate was replaced with membership to the Commonwealth of Nations, as an independent nation. The capital and largest city is Nuku'alofa. The population of Tonga in the 2011 census was 103,036.