878 - King Alfred the great won Battle of Edington

England
King Alfred united his people for a last desperate fight and in the bloody battle at Etandum (Between the towns Asdown and Chippenham), Alfred the great won the battle and he then entered Chippenham where he forced viking chief Guthrum to be baptized and become a Christian.
Ravenbanner captured from Danes in 878
The treaty of Wedmore established the Danelaw.
The Ravenbanner was mentioned 
Wales
Viking soldiers of fortune was hired by Hywel ab Ieuaf ab Idwal the Bald , they destroyed the Church of Clynnog Fawr and attacked the Lleyn territory in Gwynedd.
The Welsh usurpation Hywel had hired the vikings to assist in his desire for the throne of Gwynedd.