O'Melaghlin (Ó Máel Shechlainn), Cairbre (c.1260–1290), king of west Meath, son of Art O'Melaghlin (d. 1283), king of west Meath, was born into a house renowned for its opposition to the English: his grandfather, Cormac O'Melaghlin (qv) (d. 1239), had earned legendary status among the Irish during the early 1200s, and his father Art proved himself an indomitable foe of the English of the midlands – it was claimed in his obit that he destroyed twenty-seven castles. It is clear that his father and many of their dynasty valued Cairbre's military prowess, which led to his election to the kingship when Art died in 1283. By the end of that year Cairbre had formed an alliance with the O'Connor Falys (Uí Chonchobair Failge) of Offaly, whose strong leaders, the brothers Muirchertach O'Connor Faly (qv) (d. 1305) and An Calbach O'Connor Faly (qv) (d. 1305), aided his rise to prominence. Under this triumvirate the conflict in the midlands escalated dramatically, steadily eroding English revenues from their Offaly lands: as early as July 1283 a Kildare jury observed that the Offaly territory of Oregan, which belonged to the O'Dunnes (Uí Duinn), had annually rendered £90. 13s. 4d. during peacetime, but was now worth less than half of that sum.
Such was the military strength of this alliance that all campaigns to curb the Irish of Offaly and west Meath failed. After the FitzGeralds’ principal manor of Lea fell to Cairbre and his O'Connor Faly allies in June 1284, the English prepared a coordinated counter-offensive against Offaly, but in a series of clashes in 1285 the Irish, under Cairbre, were victorious, routing several expeditions sent against them; they destroyed a force led by Gerald fitz Maurice FitzGerald (qv) (d. 1287), 4th lord of Offaly, and took fitz Maurice prisoner. In 1286 the capture of An Calbach O'Connor Faly forced the O'Connor Falys to make peace, but the unrest continued and the region slid back into warfare by summer 1288. To counter the threat posed by the midland Irish, the justiciar, John of Sandford (qv), archbishop of Dublin (d. 1293), called up the royal service due from Leinster and attacked the Irish of Laois and Offaly. In April 1289 he invaded west Meath from Connacht, with a large force that included Maghnus O'Connor (Ó Conchobair) (d. 1293), king of Connacht, and Domnall O'Kelly (qv) (d. 1295), king of Uí Maine. They were confronted by Cairbre, the O'Molloys (Uí Máel Muaid), the MacGeoghegans (Méig Echagáin), and the Foxes (Sinnaig Uí Catharnaig) and were heavily defeated. Further south Peter Bermingham (qv) (d. 1309) and John fitz Thomas FitzGerald (qv) (d. 1316) clashed with An Calbach O'Connor Faly and ‘the rest of the princes of Leinster’ after May 1289; the O'Connor Falys, the O'Mores (Uí Mordha), and Cairbre fell on fitz Thomas's force deep inside Offaly, fitz Thomas was captured, and Sandford had to come to his rescue. After these setbacks Sandford temporised with the Irish while he assembled another army. A parley at Aghaboe, Co. Laois, failed, and in September 1289 Sandford attacked the Irish of Laois and Offaly, subduing them and bringing the war to a successful close by 5 October.
Cairbre died in 1290 at the hand of a fellow chieftain in Meath David MacCoghlan (Mac Cochláin), lord of Delvin, an act that shook the Irish midlands and outraged Richard de Burgh (qv) (d. 1326), earl of Ulster and lord of Connacht, who took revenge by devastating MacCoghlan's lands. The annals also record that the earl encouraged the killing of David MacCoghlan by the Berminghams in 1293. The death of Cairbre marked a decisive turning-point in his dynasty's fortunes. His son and successor, Murchadh, died of natural causes in 1293, opening the way for the O'Connor Falys to become the great Irish regional power.