The first Viking raid on Ireland, on an Island off the Dublin coast, occurred in 795, graduating to fortified settlements at Dublin and Annagassan by the 840s. The Vikings were twice expelled, in 866 and 902, but on each occasion returned. Between 914 and 922, the Vikings established a string of coastal settlements from Dublin to Limerick, but attempts to create a unified Norse colony failed. As the century progressed, the Viking colonies were increasingly threatened by Irish warlords. Dublin was sacked in 944, and the Norse sought powerful local allies to maintain their foothold. They chose to back the king of Leinster in eastern Ireland against the emerging strongman, Brian Boru, king of Munster, southern Ireland. It proved a catastrophic choice, with Boru decisively defeating Leinster and their Viking allies. A Viking presence lingered until 1171, but after Clontarf, it was essentially commercial with little military significance.
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