The Sultanate of Brunei's influence peaked between the 15th and 17th centuries, when its control extended over coastal areas of northwest Borneo and the southern Philippines. Internal strife over royal succession, colonial expansion of European powers, and piracy subsequently brought on a period of decline. In 1888, Brunei became a British protectorate; independence was achieved in 1984. The same family has ruled Brunei for over six centuries, and in 2017, the country celebrated the 50th anniversary of Sultan Hassanal BOLKIAH’s accession to the throne. Brunei has one of the highest per-capita GDPs in the world, thanks to extensive petroleum and natural gas fields.