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.
Ímar
Norse contact with Scotland predates the first written records in the 8th century, although the nature and frequency of these contacts is unknown. Excavations on the island of Unst in Shetland indicate that Scandinavian settlers had reached there perhaps as early as the mid-7th century and from 793 onwards repeated raids by Vikings on the British Isles are recorded. "All the islands of Britain" were devastated in 794 with Iona being sacked in 802 and 806. The Frankish "" may record the conquest of the Inner Hebrides by Vikings in 847. Scholarly interpretations of the period "have led to widely divergent reconstructions of Viking Age Scotland", especially in the early period, and Barrett has identified several competing theories, none of which he regards as proven. Ó Corráin notes: "when and how the Vikings conquered and occupied the Isles is unknown, perhaps unknowable".