http://www.pcgamer.com/total-war-saga-unveils-thrones-of-britannia-due-next-year/

In July, Total War creators Creative Assembly announced Total War Saga—a new branch of its familiar historical war tales that will "focus on a specific point in history", against the base games' overarching eras. Now, the developer has revealed Thrones of Britannia, a spin-off that's due next year. 

Set in 878AD on the British Isles, Thrones of Britannia takes place following the Viking Invasion of Britain. "The Norse warloards are firmly established," so says publisher Sega,  "but the ambitious kings of England, Ireland, Scotland and Wales have aspirations of their own—not least the great King Alfred of Wessex."