When Henry II accepted the Leinster king Diarmait Mac Murchada as his liegeman in 1166, he forged a bond between the English crown and Ireland that has never been undone. Ireland was to be changed forever as a result of the momentous events that followed – so much so that it is normal for professional historians to specialise in either the pre- or post-invasion period. Here, for the first time, is an account of the impact of the English invasion on the Irish kingdoms in the context of their strategies across the whole twelfth century. Ireland’s leading men battled for spheres of influence, for recognition of their hegemonies and, ultimately, for the coveted title of ‘king of Ireland’. But what did it mean to be the king of Ireland when no one dynasty had secured their hold on it? This book takes a close look at each pretender, asking what it meant to them – and whether the political dynamics surrounding the role had an impact on the course of the invasion itself.