Tonga is part of Polynesia and consists of about 150 islands, divided into three main groups. It was settled by people who migrated from South-East Asia some 6000 years ago, and is probably the oldest inhabited archipelago in the region. In the 12th century, Tongans were known across the Pacific as navigators and adventurers. In the 19th century, Tonga was united into a kingdom. It came under British protection in 1900, and joined the British Commonwealth as an independent monarchy, which had never lost its internal governance. Tonga's population is ethnically very homogenous. The society is made up of nobles, a caste of elite, and the common people, who are mostly poor. The king (or queen) is revered by all. The land is the property of the crown, and is distributed according to a system that guarantees some equal treatment for the commoners. The economy is based on farming and the export of cash crops, and on tourism. Many Tongans live in New Zealand, Australia and the USA. Migration is to some extent a safety valve to avoid over-population of the limited land area. The Free Wesleyan Church (Methodist) is the largest church. Together with the Catholic Church and the small Anglican community it has formed the national council of churches. Other churches are the Constitutional Church and the Anglican Church, which is part of the diocese of Polynesia. The Assemblies of God (Pentecostal) and other charismatic groups have grown much faster than the larger churches, but remain relatively small. The Tonga Evangelical Union is affiliated with the WEA.