In 1166, Ireland's High King and Mac Murchada's main ally
Muirchertach Ua Lochlainn had fallen, and a large coalition led by
Tigernán Ua Ruairc (Mac Murchada's arch enemy) marched on
Leinster. The new
High King Ruaidrí Ua Conchobair deposed Mac Murchada from the throne of Leinster. Mac Murchada fled to Wales and from there to England and France seeking the support of
Henry II of England in the recruitment of soldiers to reclaim his kingship. Henry authorised Diarmait to seek help from the soldiers and mercenaries in his kingdom. Those who agreed to help included
Richard de Clare and half-brothers
Robert FitzStephen and
Maurice FitzGerald. Robert was accompanied by his half-nephew
Robert de Barry. Strongbow was offered Diarmait's daughter
Aoife in marriage and promised the kingship of Leinster on Diarmait's death. Robert and Maurice were promised lands in
Wexford and elsewhere for their services. On returning to Wales,
Robert FitzStephen helped him organise a mercenary army of English and Welsh soldiers. Landing at
Bannow Bay, they laid
siege to Wexford which fell in May 1169. After a period of inactivity, they went on to raid the
Kingdom of Ossory. They then launched raids in the territories of the Uí Tuathail, the Uí Broin, and Uí Conchobhair Failghe. Mac Murchada gambled that King
Ruaidrí would not hurt the Leinster hostages which he had, which included Mac Murchada's son, Conchobar Mac Murchada. Although he had been distracted by disturbances elsewhere in the kingdom, King Ruaidrí could no longer ignore this powerful force. He marched his forces into Leinster and, with the mediation of the Church, the commanders of the two armies began negotiations at
Ferns, Diarmait's political base. An agreement was reached, whereby Diarmait was allowed to remain King of Leinster with Diarmait for his part recognising Ua Conchobair as High King. Some historians maintain that the treaty with Ua Conchobair included a secret agreement whereby Diarmait undertook to bring in no more foreign mercenaries and to send away
Robert FitzStephen and his men as soon as Leinster was subdued. It's possible that Mac Murchada's hand may have been forced by the arrival at
Wexford in May 1170 of
Maurice FitzGerald, Lord of Llanstephan and his force of 10 knights, thirty men-at-arms and a hundred archers and foot soldiers. Mac Murchada and FitzGerald marched on the Ostman
Norse–Gaelic city of
Dublin which surrendered. Within a short time, all Leinster was again in Mac Murchada's control. Emboldened by these victories, he sent Robert FitzStephen to the assistance of his son-in-law,
Domnall Mór Ua Briain, the
King of Thomond. In the opinion of some historians, Mac Murchada's plans may have been limited to the recovery of his throne; only later when the superiority of the mercenary arms had overawed the
Gaelic nobility of Ireland did he consider tilting at the high kingship itself. According to the contemporary
Gerald of Wales, he was advised by
Robert FitzStephen and
Maurice FitzGerald to write to Strongbow requesting assistance. Strongbow sent an advance party under
Raymond le Gros, arriving himself in 1170 at the Ostman
Norse–Gaelic settlement of
Waterford. Following the fall of Waterford, the promised marriage of Aoife and Strongbow took place. As a result, Richard FitzGilbert, count of Strigoil, became lord of Leinster. The marriage was imagined and painted in the
Romantic style in 1854 by
Daniel Maclise. '' (1854) by
Daniel Maclise, a romanticised depiction of the union between Aoife and
Richard de Clare in the ruins of
Waterford ==Death and historical aftermath==