Military history of Ireland
The Vikings pillaged monasteries on Ireland's west coast in 795, and then spread out to cover the rest of the coastline. The north and east of the island were most affected. During the first 40 years, the raids were conducted by small, mobile Viking groups. From 830 on, the groups consisted of large fleets of Viking ships. From 840, the Vikings began establishing permanent bases at the coasts. Dublin was the most significant settlement in the long term. The Irish became accustomed to the Viking presence and culture and in many cases became allies, with intermarriage common throughout Ireland. A major Irish battle involving Vikings was fought at the Battle of Clontarf in 1014, in which a large force of Vikings and their Irish allies were defeated by the gathered Irish forces of Brian Boru, then the High King of Ireland along with a small contingent of Viking defectors. After this date Viking activity was sporadic with various Kings and nobles attempting to extend their power base. In 1099, Magnus Barefoot, the King of Norway, and his Viking army had successfully campaigned alongside their Irish allies against opposing Irish warbands. On his return his force was ambushed and killed on the north coast of Ireland.
Viking Age
The term Varangian remained in usage in the Byzantine Empire until the 13th century, largely disconnected from its Scandinavian roots by then.
Having settled Aldeigja (Ladoga) in the 750s, Scandinavian colonists were probably an element in the early ethnogenesis of the Rus' people, and likely played a role in the formation of the Rus' Khaganate. The Varangians (Varyags, in Old East Slavic) are first mentioned by the Primary Chronicle as having exacted tribute from the Slavic and Finnic tribes in 859. It was the time of rapid expansion of the Vikings in Northern Europe; England began to pay Danegeld in 859, and the Curonians of Grobin faced an invasion by the Swedes at about the same date.
In 862, the Finnic and Slavic tribes rebelled against the Varangian Rus, driving them overseas back to Scandinavia, but soon started to conflict with each other. The disorder prompted the tribes to invite back the Varangian Rus "to come and rule them" and bring peace to the region. This was a somewhat bilateral relation with the Varagians defending the cities that they ruled. Led by Rurik and his brothers Truvor and Sineus, the invited Varangians (called Rus') settled around the town of Novgorod (Holmgard).