Dances in Tongan culture had a number of functions. There were, and still are, dances to show allegience to tribal chieftans, a dance performed only before the king, dances performed at marriages, war dances, etc. Some dances are performed standing, and some sitting. They are usually dances which tell a story.
Christian missionaries in Tonga did not support the colonial power's distatse for the native dances. Both the Methodist and Roman Catholic churches used indigenous dance to tell Christian stories, since the native dances were used to tell historical and cultural stories anyway. The Catholics, especially, supported the traditional dance culture.
Many dances today are performed essentially as tourist attractions, but dance is still a big part of social and cultural life in Tonga. Among the ancient dances still performed today are 'otuhaka, a dance for the king; tau'olunga, a wedding or social function dance; and several more.
Since the Tongan language was unwritten until well into the 19th century, the earlier history of the dances in somewhat vague. Check the links below.