840sCenturies: 8th century - 9th century - 10th century
- After the death of Louis the Pious, his sons Charles the Bald, Louis the German and Lothair II fight about the division of the empire until the treaty of Verdun (843).
- The Pictish kingdom and the Scottish kingdom of Dalriada are unified. The unified kingdom is called Alba.
- Viking raid of Western Francia (France) (845).