839 - Vikings expanded Picts were defeated

Frisia was attacked by a viking fleet
Vikings stayed for the winter 839-40 in Ireland after a series of great victories against the Irish. They mad a camp at Lough Neagh which they occupied for 3 years. Vikings overwintered for the first time in the newly established longphort in Dublin.
Vikings also defeated the Picts in their own kingdom. In a major battlet the Ulster chronicle tells us that, the Vikings killed most all of the Pictish nobles and the king of Picts Eogann mac Oengusa and Áed mac Boanta the king of the Scottish kingdom Dál Riata.The Picts in Scotland never recovered and the possibility of a counter-invasion disappeared.

In 839 Swedish vikings reached Miklagaard (Istanbul), they did not manage to sack the city.