In 1302 Bruce married Elisabeth de Burgh, daughter of the Earl of Ulster. The Earl was a staunch supporter of Edward I. In 1315, a famine and an invasion by a Scottish army led by Edward Bruce (brother of Robert Bruce) marked the start of the decline of the Norman colony. For 1328, A great army was led by the Earl of Ulster, Turlough O'Conor, King of Connaught, and Murtough O'Brien, King of Munster, against Brian Bane O'Brien. By 1333, the Norman territory west of the Bann was mostly lost, and the earldom consisted of five bailiwicks: Twescard (Coleraine and the Bush valley), Antrim, Carrickfergus, Blathewyc (Newtownards) and Down. From about 1333 onwards, the Anglo-Irish colony in Ireland began to decline, and eventually became restricted to the area around Dublin, (known as the Pale) and to the regions controlled by the Anglo-Irish barons of Kildare, Desmond and Ormond. Richard II came to Ireland in 1394 and 1399, but factors such as the Hundred Years War with France, the Black Death, the Wars of the Roses, and the general economic decline in Europe, meant that England was unable to maintain an effective army in Ireland for over 150 years.
The Three Baronies: Dartry, Farney, and the Lucht Tighe. In the 13th century the family of MacMahon (MacMathghamnha) held the superior authority with the title King of Oriel. The family of Eoghan MacMahon ruled Dartry from their fort at Lisnagore, near Clones. Livingstone describes these as the Dartry MacMahons. The descendents of Reamonn MacMahon ruled the northern part of MacMahon's Countrie, also known as the Lucht Tighe, from Monaghan. Livingstone calls them the Monaghan MacMahons. The descendents of Red Hugh MacMahon remained powerful in Farney, headquartered at Lurgans and then at Lisanisk, near Carrickmacross. These became known as the Farney MacMahons.
The territory of the Ui Tuirtre was also said to have included an area west of Lough Neagh (in modern co. Tyrone), as well as northwest of the great Lough in the modern barony of Loughinsholin, co, Derry. Loughinsholin itself is said to derive from the "lough of the island of the O'Lynns", i.e. the O'Flynn, chiefs of Uí Tuirtre. Groups of the Uí Tuitre were apparently driven east across the river Bann by the rise of the O'Cahans about the 12th century, and are later recorded in the central baronies of Co. Antrim, i.e. Toome and Antrim. The Uí Tuirtre genealogy goes back to Fiachu Tuirtri, son of Colla Óiss (Uais). After this time the O'Flynns (O'Lynns) were dominant chiefs of Uí Tuirtre, they being claimed as a senior branch of Clanna Rury of Ulidia. The general opinion was that the territory of Oirghiall, or Oriel, comprised the present counties of Louth, Armagh and Monaghan, and that Uladh or Ulidia, the circumscribed territory of the Clanna Rury, was, when formed into shire-ground, styled the County of Down, from Down, its principal town and Burren, a district in the Clare country named after the clan name of the O'Loughlins and the O'Connors of Corca Modhruaidh descendants of Fergus mac Roich, grandson of Ruadri Mor, founder of Clanna Rory in Ulster. The neighboring territory of Fear Li (Fir Li) was in the barony of Coleraine (northeast co. Derry), and the O'Flynns (O'Lynns) are cited holding the kingship of both Tuirtre and Fir Li, at various times. O'Dugan (Poems) in the Orghialla section of his poem cite O'Floinn and O'Domhnallain as lords of Uí -Tuirtre. Francis Byrne in his Irish Kings and High Kings states the Uí Maic Caírthinn south of Lough Foyle, the Uí Fiachrach Arda Sratha and Uí Thuirtri west and east of the Sperrins were collectively known as the Uí Macc Uais. The Northern Uí Fiachrach were seated in Breifne what are now the counties of Mayo and Sligo.
Scottish and Irish clans historically descended from Colla Uais include: (a) Scotland: MacDonald, MacGregor, MacGillivray, MacEachern, MacMillian, MacKinnon, MacQuarrie, Campbell, MacPhee, MacInnes; (b) Ireland: Maguire, MacMahon, MacManus, Agnew, Alexander, Boylan, Cassidy (who were chiefs of Coole), Connolly (chiefs in Fermanagh), Duffy, Hale, Hanratty (anglicized Enright), Keenan of Fermanagh, Leahy in Galway, MacCabe of Monaghan and Caven, MacCann of Clan brassil, MacEvoy, MacVeagh, MacVeigh (anglicized form of MacUais) in West Meath, Magee in Down and Antrim, MacKenna in Monaghan, MacOscar (anglicized MacCusker), MacTully, and MacGrath in Fermanagh, MacNeny (anglicized Bird), MacRory (anglicized Rogers), MacSheehy, Madden, Norton, O’Carroll, O’Flanagan, O’Hanlon, O’Hart in Tara, and MacQuillan in Antrim.
The part of Orgiall was overrun by the forces of John de Courcy (Chester and Somerset) in the reign of King John, but the MacMahons maintained their national independence to the reign of Elizabeth, when Monaghan was formed into a county, so called from its chief town Muineachan, that is, the Town of Monks. De Courcy brought in by one of two feuding minor Irish Kings, Dermot MacMurrough of Leinster and Tiernan O'Rourke of Breifne. His great-grandfather, Richard de Curci came to England with William the Conqueror and is named in the Domesday Book. After his two battles at Down, de Courcy moved north to the territory of the Dal nAraide, whose king he killed. He then attacked Cu Mide Ua Floinn, a powerful king in county Antrim. He reached the north coast at Coleraine. De Courcy divided the newly Lecale among his Knights. Many of the names of those soldiers are still to be found in Lecale and elsewhere in Eastern Ulster today; some in families, some in placenames eg Savage, Russell, FitzSimon, Jordan, White, McMahon, Hackitt, Copeland, Audley. With the exception of the Savages, who had land on the Ards peninsula and retained their influence for many centuries, few of the recipients of de Courcy's land allocations survived his defeat by Hugh de Lacy in 1204. Of those who did so and transferred their loyalty to de Lacy, many were deprived of their land by King John when in 1210 he took over de Lacy's earldom. In 1180, de Courcy married Affreca de Galloway, the daughter of Godred, the Norse King of the Isle of Man. Inch abbey was founded by John de Courcy in recompense for burning down the abbey of Erenagh in 1177. The remaining monks of Erenagh appear to have had this new monastery founded for them in 1180, when they were affiliated to Furness Abbey in Lancashire. The Cistercian order at Rushen had its beginning in 1098, though, probably, they were not planted here till six-and-thirty years after, by Evan, abbot of Furness and at Maughold, in the changes of time, when the glories of the Norman church gave place to the primitive constitution of the Celtic Fathers, the sons of St. Bernard, from the mother-house of Furnes-Abbey, became the guardians of the Faith in Man. In 1199, King John authorized Hugh de Lacy, younger son of the Lord of Meath, to wage war on John de Courcy. In May 1205, King John made Hugh Earl of Ulster. Dunluce may have been built about 1200 by Richard de Burgh, Earl of Ulster. John de Courcy returned, sailing across the Irish sea from the Isle of Man in July 1205 with Norse soldiers and a hundred boats supplied his brother-in-law, Ragnold, King of Man. John and his army landed at Strangford and laid siege to Dundrum Castle in vain, because the defenses he himself had made were too strong.
The noble families now in Monaghan, are the Dawsons, barons of Cremorne; the Westenras, lords Rossmore; and the Blayneys, lords Blayney. The other chief landed proprietors are the families of Shirly, Lesley, Coote, Corry, and Hamilton.
In the ancient ecclesiastical divisions the territory of Orgiall was comprised within the diocese of Clogher (Bishops); but in the 13th century the county of Louth was separated from Clogher and added to the diocese of Armagh. In early times there were bishops' sees at Clones and, Louth, which sees were afterwards annexed to Clogher. In the early writers we find the bishops of Clogher frequently styled bishops of Orgiall and Ergallia. At present the diocese of Clogher comprises the whole of Monaghan, the greater part of Fermanagh, parts of Donegal and Tyrone, and a small portion of Louth. The see of Armagh, founded by St. Patrick in the 5th century, became the seate of an archdiocese, and the metropolitan see of all Ireland. The diocese of Armagh comprehends the greater part of that county, with parts of Louth, Meath, Tyrone, and Londonderry, and has ecclesiastical jurisdiction over the sees of Meath, Ardagh, Kilmore, Clogher, Raphoe, Derry, Down and Conor, and Dromore.