Norman and French barons, with Welsh followers, and Flemings from Pembroke, led the invasion that began in 1169. They were men trained to war, with armour and weapons unknown to the Irish. But they owed no small part of their military successes in Ireland to a policy of craft. If the Irish fought hard to defend the lands they held in civil tenure, the churches had no great strength, and the seizing of a church estate led to no immediate rising out of the country. The settled plan of the Normans, therefore, was to descend on defenceless church lands, and turn them into Norman strongholds; in reply to complaints, they pleaded that the churches were used by the hostile Irish as storing places for their goods. Their occupation gave the Normans a great military advantage, for once the churches were fortified and garrisoned with Norman skill the reduction of the surrounding country became much easier. The Irish during this period sometimes plundered church lands, but did not occupy, annex, or fortify them. The invaders meanwhile spread over the country. French and Welsh and Flemings have left their mark in every part of Ireland, by Christian names, by names of places and families, and by loan-words taken into Irish from the French. The English who came over went chiefly to the towns, many of them to Dublin through the Bristol trade. Henry II himself crossed in 1171 with a great fleet and army to over-awe his too-independent barons as well as the Irish, and from the wooden palace set up for him in Dublin demanded a general oath of allegiance. The Normans took the oath, with some churchmen and half-a-dozen Irish chiefs.
In Henry's view this oath was a confession that the Irish knew themselves conquered; and that the chief renounced the tribal system, and handed over the land to the king, so that he as supreme lord of all the soil could allot it to his barons, and demand in return the feudal services common in Normandy or in England. No Irish chief, however, could have even understood these ideas. He knew nothing of the feudal system, nor of a landlord in the English sense. He had no power to hand the land of the tribe over to any one. He could admit no "conquest," for the seizing of a few towns and forts could not carry the subjection of all the independent chiefdoms. Whatever Henry's theory might be, the taking of Dublin was not the taking of an Irish capital: the people had seen its founding as the centre of a foreign kingdom, and their own free life had continued as of old. Henry's presence there gave him no lordship: and the independent temper of the Irish people was not likely, after their Danish experience, to be cowed by two years of war. Some cunning explanation of the oath was given to the Irish chiefs by the subtle Angevin king and his crafty Norman counsellors--that war was to cease, that they were to rule as fully and freely as before, and in recognition of the peace to give to Henry a formal tribute which implied no dominion.