The Northern Isles (Scots:Northren Isles; Scottish Gaelic:Na h-Eileanan a Tuath; Old Norse:Norðreyjar) is an archipelago comprising a chain of islands off the north coast of mainland Scotland. The climate is cool and temperate and much influenced by the surrounding seas. There are two main island groups: Shetland and Orkney. There are a total of 26 inhabited islands with landscapes of the fertile agricultural islands of Orkney contrasting with the more rugged Shetland islands to the north, where the economy is more dependent on fishing and the oil wealth of the surrounding seas. Both have a developing renewable energy industry. They also share a common Pictish and Norse history. Both island groups were absorbed into the Kingdom of Scotland in the 15th century and remained part of the country following the formation of the Kingdom of Great Britain in 1707, and later the United Kingdom after 1801. The islands played a significant naval role during the world wars of the 20th century.