Cené l nEó gain, a royal dynasty from Inishowen in Donegal, defeated its previously more successful opponent, Cené l Conaill - also from Donegal - at the battle of Cló itech in AD 789. All changed following that battle. From then on, the Cené l nEó gain kingdom, known as ' Ailech' , spread across Counties Derry, Tyrone (giving that territory its name), into Armagh, and dominated the whole territory of Ulster. It also attained, alternately, the higher kingship of Tara. After surnames appeared c.1000, the Mac Lochlainns and O' Neills became Cené l nEó gain' s leading families. Meanwhile, the defeated Cené l Conaill struggled to maintain some degree of prestige following the emergence of a previously minor, upstart kingdom, originally from west Donegal, the Sí l Lugdach. By c.

1200 the O' Neills and the leading Sí l Lugdach family, the O' Donnells, were in position to rule the whole of Ulster until the English conquest c.1600. This book outlines in detail how that situation came about.