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 raid warfare and tactics
In Northern Europe at the start of the 8th century, Vikings began raiding coasts of the British Isles across the sea from Scandinavia, particularly monasteries, which carried a great deal of valuable treasures. The first known raid was on the Holy Island of Lindisfarne off the English coast in 793. This raid was also the first one that made a lasting impact on the British Isles and made the Anglo-Saxons aware of the Viking threat. A primary source from the raid on Lindisfarne states that there "were immense flashes of lightning, and fiery dragons were seen flying in the air". These raids continued for the entirety of the Viking Age. These initial raids had a religious implication to them. Vikings would target monasteries along the coast, raid the towns for their booty, and destroy what was left. This caused mass fear amongst such monks, as they felt that it was punishment from God. There is also the complication of a lack of direct written sources about these raids from the Viking perspective. This leads to biased views of the raiders from Christians who were being attacked in their churches and lands . From their point of view, the Vikings were violent and evil heathens.