Prior to the Anglo-Norman invasion of Ireland, the island was ruled through a system of small kingdoms. There was very little unity, with only Brian Boru, King of Munster, achieving anything like total dominion. This dissolved when he was killed defeating his rivals at the Battle of Clontarf in 1014.
The first Anglo-Norman intervention in Ireland came in 1167. Henry II of England, wary of the power his generals were amassing there, landed with a large army in 1171, and by 1175 had succeeded in gaining nominal control of most of the island.
'The centre of English power was a colony in Dublin and control was slowly exerted over Irish territory.'
Henry's motives for this first English conquest of Ireland are probably twofold: to distract from the recent murder of Thomas Becket, Archbishop of Canterbury; and because the English pope, Hadrian IV, had conferred on him the title 'lord of Ireland' with the intention that Henry should take control of the island and reform its church.
The centre of English power was a colony in Dublin and up to the middle of the 13th century, control was slowly exerted over Irish territory. But the colonists were never quite able to totally subdue the island, and much intermingling of the English and Irish populations took place.
By the middle of the 14th century much of the island had reverted to Irish control through conquest. In 1315, Edward Bruce, brother of the Scottish king Robert the Bruce, was invited to lead the expedition to finish off the Normans. He failed and was killed in battle in 1318. Nonetheless, the English colony in Dublin was in dire straits.
Richard II of England was the next monarch to set foot in Ireland, but his attempt to gain control proved a fatal distraction. He was deposed and murdered on his return from Ireland in 1399.