Henry, on his part, was only too eager to accept his new responsibility, and less than a year after his coronation he called a council to discuss the conquest of Ireland. The scheme was abandoned on account of its difficulties, but the question was later raised again in another form. Diarmait Mac Murchadha (in modern form Jeremiah Murphy), King of Leinster, had carried off in 1152 the wife of the chief of Breifne (Cavan and Leitrim). A confederation was formed against him under Ruaidhri (or Rory), King of Connaught, and he was driven from the island in 1166. "Following a flying fortune and hoping much from the turning of the wheel," he fled to Henry in Aquitaine, did homage to the English king for his lands, and received in return letters granting permission to such of Henry's servants as were willing to aid him in their recovery. Diarmait easily found allies in the nobles of the Welsh border, in whose veins ran the blood of two warlike races. It was by just such an enterprise as this that their Norman fathers and grandfathers had won their Welsh domains. From childhood they had been brought up in the tumult of perpetual forays, and trained in a warfare where agility and dash and endurance of hunger and hardship were the first qualifications of a soldier. Richard de Clare, Earl of Striguil, in later days nicknamed Strongbow - a descendant of one of the Conqueror's greatest warriors, but now a needy adventurer sorely harassed by his creditors - was easily won by the promise of Diarmait's daughter and heiress, Aeifi, as his wife. Rhys, the Prince of South Wales, looked favourably on the expedition. His aunt, Nesta, had been the mistress of Henry I. of England; and had afterwards married first Gerald of Windsor, and then a certain Stephen; her sons and grandsons, whether Fitz-Henrys, Fitz-Geralds, or Fitz-Stephens, were famous men of war; nor were the children of her daughter, who had married William de Barri, behind them in valour. No less than eighteen knights of this extraordinary family took part in the conquest, where in feats of war they renewed the glories of their ancestors both Norse and Welsh; a son of Nesta's, David, the Bishop of St. David's, gave his sympathy and help; while her grandson, Gerald de Barri, became the famous historian of the conquest.
In 1167 Diarmait returned to Ireland with a little band of allies, the pioneers of the English conquest. Others followed the next year, among them Strongbow's uncle, Hervey of Mount Moriss, a famous soldier in the French army, distinguished for his beautifully proportioned figure, his delicate long hands, his winning face, and graceful speech. With him went Nesta's son Robert Fitz-Stephen, a powerful man of the Norman type, handsome, freehanded, sumptuous in his way of living, liberal and jovial, given to wine and dissipation. His nephew, Meiler Fitz-Henry, showed stronger traces of Welsh blood in his swarthy complexion, fierce black eyes, and passionate face. The knights carried on the war with the virtues and vices of a feudal chivalry, with a frank loyalty to their allies, a good comradeship which recognized no head but left each knight supreme over his own forces, a magnificent daring in the face of overwhelming forces, and a joyful acceptance of the savage privileges of slaughter and rapine which fell to their lot. "By their aid Diarmait began first to take breath, then to gain strength, and at last to triumph over his enemies." The Irish, however, rallied under the king of Connaught against the traitor who had brought the English into their land; and Diarmait was forced to conclude a peace and promise to receive no more English soldiers.
Meanwhile other knights were preparing for the Irish expedition. Maurice Fitz-Gerald encamped on a rock near Wexford. Another Fitz-Gerald, Raymond the Fat, fortified his camp near Waterford. In August 1170 came Earl Richard himself, who had crossed to France in search of Henry, and with persistent importunity implored for leave to join the Irish war. Henry, at that moment busy in his last negotiations with Thomas, gave a doubtful half-consent, and Richard sailed with an army of nearly fifteen hundred men. We see in the pages of Gerald of Wales, the hero with whose name the conquest of Ireland was to be for ever associated, red-haired, gray-eyed, freckled, with delicate features like a woman's, and thin, feeble voice; wearing a plain citizen's dress without arms, "that he might seem more ready to obey than to command;" suave, gracious, politic, patient, deferential, with his fine aristocratic air, and an undaunted courage that blazed out in battle, when "he never moved from his post, but remained a beacon of refuge to his followers." At his coming Waterford was taken, as Wexford and Ossory had been before. Before the prudent Norman went farther the marriage contract was carried out, and the beginning of a strife which lasted for seven hundred years was celebrated in this first alliance of a Norman baron and an Irish chief. Richard and Diarmait marched against Dublin, and its Danishin habitants were driven over sea. In a few months their king, Hasculf, returned with a great fleet gathered from Norway, the Hebrides, the Orkneys, Man, - the last fleet of Northmen which descended on the British Isles, - but again the Normans won the day.