980 - Vikings raided England again

Denmark
The Viking ring castle Trelleborg was build in Denmark.
England
Viking raids on England again. Widespread viking raids from Ireland and Man in England until 990.

Ireland
The Battle of Tara between Southern Uí Néill and the Kingdom of Dublin ended with a devastating defeat for the Kingdom of Dublin.The loser Óláf Sigtryggsson abdicated and died on Iona. Dublin was besieged by Máel Sechnaill, who forced Dublin to surrender thralls and valuable goods, as well as give up all claims to Uí Néill held territory.
Russia
The reign of Vladimir I(Saint Vladimir)(958-1015) the first Christian duke of Kiev. He made orthodox Christianity the official religion of the Russian people.
Sweden
Eric the victorious became king of Sweden until 995. Olof Skötkonung, king of Sweden was born.
Wales
Gofraid mac Arailt  entered an alliance with king Cystennin ab Iago of Gwynedd to support Cystennin against Hywel ab Ieuaf, who was attempting to capture the Gwynedd throne for himself. The combined Welsh-Danish force devastated Anglesey from where they crossed to Lleyn and continued ravaging the peninsula until Hywel's troops confronted them in the Battle of Hirbarth,Gwaith where Cysteinn was killed.