Along with the O'Carroll of Éile, the O'Kennedy of Ormond and the Mulryan of Owney, the O'Dwyers of Kilnamanagh were one of a cluster of regional Gaelic clan powers in the High Middle Ages in the area of what would one day become County Tipperary who held out against Anglicisation with the arrival of the Lordship of Ireland. They interplayed with newer Norman arrivals on their borders who became significant powers, especially the Butler Earls of Ormond. Clan members Philip O'Dwyer and Anthony O'Dwyer captured the Rock of Cashel in 1641 during the Irish Rebellion of 1641. Subsequently, following the Cromwellian War in Ireland, the clan were punished and dispossessed of much of their land under the Act for the Settlement of Ireland 1652. Some were removed to County Clare, while others chose exile as Wild Geese on the European Continent. A significant number of O'Dwyer men found service in armies of Bourbon France, the Habsburg Monarchy (including General Count John O'Dwyer, Governor of Belgrade) and even Romanov Russia (providing an Admiral).