Tonga officially the Kingdom of Tonga is an archipelago in the south Pacific Ocean comprising 171 islands, 48 of them inhabited, stretching over a distance of about 800 km (500 mi) in a north-south line. Tonga is the only sovereign monarchy among the island nations of the Pacific Ocean, as well as being the only island nation never to have been formally colonized. First discovered by Captain Cook in 1773, the islands became a British colony from 1901 to its independence in 1970.