The martyrdom of Thomas Becket served his cause better than his continuance in life could have done. Even if his murderers foolishly thought to serve the king by their deed, Henry himself was under no delusion as to its effect. He was thunderstruck at the news, and, in a frenzy of horror which was no doubt genuine, as well as to mark his repudiation of all share in the deed, he fasted and shut himself from communication with the court for days. But the public opinion of Europe would not acquit Henry of the guilt. Letters poured in upon the pope denouncing him and demanding his punishment. The interdict of his Norman dominions which had been threatened was proclaimed by the Archbishop of Sens, but suspended again by an appeal to the pope. Events moved slowly in the twelfth century, and before the pope could take any active steps in the case, an embassy which left Normandy almost immediately had time to reach him and to promise on the part of the king his complete submission to whatever the pope should decree after examination of the facts. Immediate punishment of any severity was thus avoided, and the embassy of two cardinals to Normandy which the pope announced could act only after some delay.

In the meanwhile in England Thomas the archbishop was being rapidly transformed into Thomas the saint. Miracles were reported almost at once, and the legend of his saintship took its rise and began to throw a new light over the events of his earlier life. The preparation of his body for the grave had revealed his secret asceticism, - the hair garments next his skin and long unchanged. The people believed him to be a true martyr, and his popular canonization preceded by some time the official, though this followed with unusual quickness even for the middle ages. It was pronounced by the pope in whose reign he had died on February 21, 1173. For generations he remained the favourite saint of England, and his popularity in foreign lands is surprising, though it must be remembered that he was a great and most conspicuous martyr of the official Church, of the new Hildebrandine Church, of the spirit and ideas which were by that date everywhere in command.

This long and bitter struggle between Church and State, unworthy of both the combatants, was now over except for the consequences which were lasting, and the interest of Henry's reign flows back into the political channel. The king did not wait in seclusion the report of the pope's mission. It may have been, as was suggested even at the time, that he was glad of an excuse to escape from Normandy before the envoys' coming and to avoid a meeting with them until time had done something to soften the feeling against him. Before his departure his hold on Britanny was strengthened by the death, in February, 1171, of Conan the candidate whom he had recognized as count. Since 1166 the administration of the country had been practically in his hands; and in that year his son Geoffrey had been betrothed to Constance, the daughter and heiress of Conan. Geoffrey would now succeed to the countship, but he was still a child; and Britanny was virtually incorporated in Henry's continental empire.

The refuge which the repentant Henry may have sought from the necessity of giving an answer to the pope at once, or a kind of preliminary penance for his sin, he found in Ireland. Since he received so early in his reign the sanction of Pope Hadrian IV of his plan of conquest, he had done nothing himself towards that end, but others had. The adventurous barons of the Welsh marches, who were used to the idea of carving out lordships for themselves from the lands of their Celtic enemies, were easily persuaded to extend their civilizing operations to the neighbouring island, where even richer results seemed to be promised. In 1166 Dermot, the dispossessed king of Leinster, who had found King Henry too busily occupied with affairs in France to aid him, had secured with the royal permission the help he needed in Wales, and thus had connected with the future history of Ireland the names of "Strongbow" and Fitzgerald. The native Irish, though the bravest of warriors, were without armour, and their weapons, of an earlier stage of military history, were no match for the Norman; especially had they no defence against the Norman archers. The conquest of Leinster, from Waterford to Dublin, and including those two cities, occupied some years, but was accomplished by a few men. "Strongbow" himself, Richard de Clare, Earl of Pembroke, did not cross over till the end of August, 1170, when the work was almost completed. He married the daughter of Dermot and was recognized as his heir, but the death of his father-in-law in the next spring was followed by a general insurrection against the new rulers, and this was hardly under control when the earl was summoned to England to meet the king.