The Viking Age in Ireland began when raiding parties arrived of the east coast of Ireland in 795. Over the next twenty years Ireland was scourged by raiding parties that came in search of mobile wealth and slaves. They looted and destroyed island based monasteries and coastal communities. By the 1820's they know enough about Ireland - the language, political and military situation, the agricultural potential, geography - to begin considering an invasion and settlement. The first major invasions occurred in the 830's. The 830's until the 870's was the first of two periods when the Vikings had the potential to defeat the Irish and build their colony. The Irish fought back, often the initiative being devolved to local chieftains. Once the issue of who would be high king in Ireland was resolved, the Irish resistance evolved. The Danes arrived in the 850's and controlled Dublin until a counter-attack restored control to the Norwegians. In the 870's the Norseman lost their main leaders and this resulted in twenty years of internal warfare for control of the colony. During this period the Irish became resurgent and after a civil war amongst the Vikings the Irish acted and ousted them from all their bases culminating in the takeover of Dublin in 902.