The Anglo-Norman incursion of the late twelfth century shattered the nascent kingship of Ireland and brought a long period of decentralised warlordism in its wake. Kingship fragmented and fell back upon those regional dynasties that had contended for the national kingship. These dynasties in turn found themselves undermined by freebooting Anglo-Norman warlords and reduced to equality with their own newly-militarised minor lords. The kingly pretentions of these minor lords were likewise reinvigorated and embellished with titular claims to the kingship of long-vanished early medieval sovereignties. Yet the Anglo-Normans did not prevail in Ireland as elsewhere and the fourteenth century saw a resurgence in Irish fortunes during which many of the losses of previous centuries were reversed and the authority of the English state (in the form of a lordship of Ireland held subsidiary to the English crown) was restricted to a small enclave on the eastern coast. Though a national kingship failed to re-emerge from the patchwork of native Irish and naturalised Anglo-Norman lordships lying beyond, the leading Irish families accommodated themselves to such an idea by abandoning their antiquarian nomenclature of kingship for one of chiefship of family as marked by the use of surname as title.
The annals disclose that eleven members of the MacLochlainn family (including their leader Domhnall) were killed at the battle of Cameirge in 1241, victims of an unusually thorough slaughter that placed the family on the point of extinction. Though the genealogies trace two continuing lines of descent, through two sons of Domhnall, the annals indicate that the chiefship was held by his grandson Diarmaid by 1260 so it would appear that of the males of the family only his grandchildren survived the events of 1241. Outside of the genealogies Domhnall is also known to have had a daughter named Seisilin. Her obituary in the annals in 1250 implies that she was married to the Brian O Neill who led the O Neill family at Cameirge but, as the annals record in 1260 that Diarmaid was killed at the battle of Down fighting Anglo-Norman forces alongside Brian, it would appear that the marriage reflected a post-1241 alliance between the two leading families of Cenél nEoghain against an outside threat. This finds resonance in a contemporary poem by Giollabrighde MacConmidhe concerning the battle of Down which relates that:
Ní bhiath lagadh i Leith Chuinn
Muna marbhthaoi Mág Lochluinn
Ón lósa oighidh Bhriain bhuig
Doiligh na dhiaidh gan Diarmuid
'There would be no weakening in Leath Cuinn
If MacLochlainn had not been killed
Since the day of gentle Brian’s death
It is hard to live after him without Diarmaid'
In the poem Leath Cuinn ('Conn's Half') is a literary conceit for the northern half of Ireland, referring back to a legendary ancestor of the Uí Néill named Conn Cétchathach ('Conn of the Hundred Battles'), so it would seem that Diarmaid was considered a likely successor as ruler in the north had he survived. The text Ceart Uí Néill ('Right of O Neill') indicates that the MacLochlainn family held on to the lordship of Inishowen for some time after 1241 and this is borne out in late thirteenth and early fourteenth century annals and ecclesiastical records showing that they retained sufficient standing to participate in regional political disputes and to provide the Church with two bishops of Derry, though their influence would have been curtailed after 1301 when the Anglo-Norman earldom of Ulster reached its westernmost extent upon the erection of Northburgh castle (modern Greencastle) in northeastern Inishowen. In 1333 an English inquisition recorded that the manor of Northburgh was lost to the earldom by which time the O Doherty family seem to have extended their sphere of influence north from Tír Conaill so that in 1339 the annals describe them as effective lords of Inishowen and in 1413 as in full possession of the lordship. This appears to have left its mark as a stratum within the MacLochlainn genealogy with most lines of descent terminating around this time, presumably reflecting loss of status, leaving once again just two lines continuing. These lines continue through the brothers Aibhne and An Oifistel, the descendants of An Oifistel finding a new role as officials in the Church and the descendants of Aibhne holding on to a fragment of their former lordship that by the early seventeenth century was reduced to a small enclave defended by two castles (pictured above) on the eastern coast of Inishowen.