1168–1536

By the 12th century, Ireland was divided politically into a shifting hierarchy of petty kingdoms and over-kingdoms. Power was exercised by the heads of a few regional dynasties vying against each other for supremacy over the whole island. One of these men, King Diarmait Mac Murchada of Leinster was forcibly exiled by the new High King, Ruaidri mac Tairrdelbach Ua Conchobair of the Western kingdom of Connacht. Fleeing to Aquitaine, Diarmait obtained permission from Henry II to recruit Norman knights to regain his kingdom. The first Norman knight landed in Ireland in 1167, followed by the main forces of Normans, Welsh and Flemings. Several counties were restored to the control of Diarmait, who named his son-in-law, the Norman Richard de Clare, known as Strongbow, heir to his kingdom. This caused consternation to King Henry II of England, who feared the establishment of a rival Norman state in Ireland. Accordingly, he resolved to establish his authority.

With the authority of the papal bull Laudabiliter from Adrian IV, Henry landed with a large fleet at Waterford in 1171, becoming the first King of England to set foot on Irish soil. Henry awarded his Irish territories to his younger son John with the title Dominus Hiberniae ("Lord of Ireland"). When John unexpectedly succeeded his brother as King John, the "Lordship of Ireland" fell directly under the English Crown

Initially the Normans controlled the entire east coast, from Waterford up to eastern Ulster and penetrated far west in the country. The counties were ruled by many smaller kings. The first Lord of Ireland was King John, who visited Ireland in 1185 and 1210 and helped consolidate the Norman controlled areas, while at the same time ensuring that the many Irish kings swore fealty to him.

Throughout the thirteenth century the policy of the English Kings was to weaken the power of the Norman Lords in Ireland. For example King John encouraged Hugh de Lacy to destabilise and then overthrow the Lord of Ulster, before creating him to the Earl of Ulster. The Hiberno-Norman community suffered from a series of invasions that ceased the spread of their settlement and power. Politics and events in Gaelic Ireland served to draw the settlers deeper into the orbit of the Irish.

By 1261 the weakening of the Normans had become manifest when Fineen MacCarthy defeated a Norman army at the Battle of Callann. The war continued between the different lords and earls for about 100 years and the wars caused a great deal of destruction, especially around Dublin. In this chaotic situation, local Irish lords won back large amounts of land that their families had lost since the conquest and held them after the war was over.

The Black Death arrived in Ireland in 1348. Because most of the English and Norman inhabitants of Ireland lived in towns and villages, the plague hit them far harder than it did the native Irish, who lived in more dispersed rural settlements. After it had passed, Gaelic Irish language and customs came to dominate the country again. The English-controlled territory shrunk back to a fortified area around Dublin (the Pale), and had little real authority outside (beyond the Pale).

By the end of the 15th century, central English authority in Ireland had all but disappeared. England's attentions were diverted by the Wars of the Roses. The Lordship of Ireland lay in the hands of the powerful Fitzgerald Earl of Kildare, who dominated the country by means of military force and alliances with lords and clans around Ireland. Around the country, local Gaelic and Gaelicised lords expanded their powers at the expense of the English government in Dublin but the power of the Dublin government was seriously curtailed by the introduction of Poynings Law in 1494. According to this act the Irish parliament was essentially put under the control of the Westminster parliament.