Control of the wealthy coastal kingdom was bitterly contested during Ascall's floruit, with members of his immediate family, as well as Islesmen and Irishmen, all securing power for brief periods of time.

In the latter half of 1170, Dublin itself fell to the combined forces of Mac Murchada and the powerful English magnate Richard de Clare, Earl of Pembroke.

When an indigenous ruler was not to be found, however, the Dubliners seem to have sought leadership from the Isles, rather than endure a non-Leinster overking, as evidenced by the attempt to install Gofraid.

[43] The latter campaign, recorded by the Annals of Ulster,[44] and the thirteenth- and fourteenth-century texts Brut y Tywysogyon[45] and Brenhinedd y Saesson,[46] concerned naval manoeuvres off Wales, in the service of Henry II, King of England.

[47] The former campaign, recorded by the Annals of Ulster,[48] consisted of involvement in the ill-fated invasion of mainland Scotland, launched by Somairle mac Gilla Brigte, King of the Isles.

[55] In fact, Dublin appears to have formed a key part of Ua Conchobair's arsenal, and it is apparent that Mac Murchada was doomed without the support of this coastal-kingdom.

[56] Certainly, the twelfth- to thirteenth-century La Geste des Engleis en Yrlande relates that Ascall ("MacTurkyl de Diveline") had abandoned his former overlord,[57] and the eleventh- to fourteenth-century Annals of Inisfallen specify that Mac Murchada was only expulsed from Ireland after the Leinstermen and Dubliners had turned against him.

[62] Ua Conchobair responded by penetrating Uí Chennselaig in a campaign, recounted by the fourteenth-century Annals of Tigernach, that included military support from Dublin.

[64] The situation in Ireland remained relatively unchanged until the arrival of a significant force of mercenaries in the summer of 1169, after which some of Mac Murchada's former vassals began to come over to his side.

[71] According to La Geste des Engleis en Yrlande, however, the kings of Uí Fáeláin and Osraige, and Ascall—described by this source as the "lord" of Dublin—stubbornly refused to support Mac Murchada's cause.

[73] The following year, however, saw the arrival of even more English support for Mac Murchada; and in August 1170, Richard de Clare, Earl of Pembroke landed in Ireland and took Waterford by storm.

[76] If the account of the Annals of the Four Masters is to be believed, the Dubliners switched sides at this point, deserted the cause of Ua Conchobair, and further suffered an act of divine justice as their town went up in flames.

[89] The account of events recorded by Expugnatio Hibernica and La Geste des Engleis en Yrlande indicate that Ascall's forces consisted of heavily armoured Islesmen and Norwegians.

[92] According to both sources, Ascall's followers included a notable warrior named "John the Mad",[93] a figure who may or may not be identical to the Orcadian saga-character Sveinn Ásleifarson.

[94][note 11] According to La Geste des Engleis en Yrlande, the invaders made landfall at the "Steine", located on the southern bank of the River Liffey, and proceeded to encamp themselves outside the town's walls.

[106] Both sources relate that the town's defenders, led by Cogan and his brother Richard, successfully repulsed the invaders, slew John, and captured Ascall as he fled to his fleet.