In 1066, William the Conqueror's Norman-French army defeated Harold, King of England, at the Battle of Hastings and William claimed the English crown as his own.

A Century later, William's great-grandson, Henry II, was the first English King to set foot on Irish soil when he landed at Waterford with his invading army.

Dermot MacMurrough, the exiled King of Leinster, had initiated the Norman invasion of Ireland two years earlier by requesting Henry's assistance in regaining his throne. In 1169, MacMurrough and the Norman forces landed in Ireland and were soon victorious.

MacMurrough secured his position by naming his son-in-law and loyal Norman knight (named 'Strongbow') as his heir. Henry, however, fearing this rival Norman state may threaten the English throne, led his troops into Ireland in 1171, forcing the Irish Kings to submit to his authority. In 1185, Henry's youngest son, John, was awarded the Irish territories and the title Lord of Ireland; these in turn became the possessions of the English Crown when John succeeded his brother to the throne in 1199.