The Earldom of Ulster grew to be the most powerful territorial unit in Anglo-Norman Ireland by the end of the thirteenth century; yet from the mid-fourteenth century onward, the earldom went into decline, suffering a dramatic reduction in its territorial extent, and the original Anglo-Norman settlers—who became increasingly Gaelicized—lost virtually all contact with the central government in Dublin.
Control of the territory that eventually became the earldom of Ulster was first won by John de Courcy in 1177 from the ancient Mac Duinn Sleibe dynasty of Ulaid. De Courcy’s conquest, which roughly comprised the modern counties Down and Antrim, was consolidated with settlement from England, notably from Cumbria—just over seventy miles away across the Irish Sea—where de Courcy had family connections. De Courcy ruled Ulster with exceptional independence for over twenty-five years until, in 1205, he was expelled by Hugh II de Lacy (d. 1242). De Lacy was rewarded by King John with de Courcy’s lands, and it was at this point that Ulster became the colony’s first earldom. De Lacy was himself expelled by King John during his expedition to Ireland of 1210, for association with the king’s enemies. De Lacy was not restored until, in the 1220s, he resorted to open war with the government. In 1227, he was confirmed as earl of Ulster for life, so that when he died in 1242, the earldom reverted to the crown.
By this time, the earldom had developed into the five administrative areas of Down, Antrim, Carrickfer-gus, Newtown Blathewyc (Newtownards), and Cole-raine. The borders of these regions were not precisely defined and fluctuated periodically, but the earldom protected itself by densely covering the landscape with mottes, although rarely with the accompanying bailey. There were important castles at Dundrum, Greencastle (Co. Down), and Coleraine. The impressive fortress at Carrickfergus was a royal castle and remained garrisoned to the end of the Middle Ages. Ulster held liberty jurisdiction, meaning that, with only minor exceptions, the earls ruled independently of the crown and kept separate administrative records. These records were stolen from Trim Castle in the 1490s, and their loss may partly explain why the earldom has been so neglected by historians of the Irish lordship. Fortunately, royal records afford a glimpse into its workings during the periods when the earldom lapsed or the earl was a minor.
Ulster remained in the king’s hands from the death of de Lacy until, in 1263, it was granted to the lord of Connacht, Walter de Burgh. Walter died in 1271 and was succeeded by a minor, Richard de Burgh (d. 1326), the "Red Earl." Richard gained control of Ulster in 1281, and during his tenure the earldom reached the height of its territorial extent and influence. Richard’s control extended west of the river Bann to Derry, and he built Northburgh Castle on the Inishowen peninsula. He gained the submission of all the native Ulster lords except Ua Domnaill, claiming from them military service known as the "bonnaght" of Ulster (from buana, a hired soldier).
The career of the "Red Earl" illustrates how Ulster, far from being a peripheral region, was part of a wider political community linked by the Irish Sea. As noted, de Courcy colonized Ulster from the north of England. Following de Lacy’s forfeiture in 1210, large tracks of the earldom’s coastline were granted to the Scottish earls of Athol, Carrick, and the lord of Galloway. This interconnection was perpetuated under de Burgh, who captured the Isle of Man for Edward I in 1290 and served with his Gaelic retinue in Scotland in 1296 and 1303. He was, moreover, linked by marriage to the Bruces—earls of Carrick and future kings of Scotland— whose claims to land in the earldom cannot have been forgotten when between 1315 and 1318 Ulster was the base for Edward Bruce’s attempt to claim the kingship of Ireland. When, in 1328, Richard de Burgh’s grandson William (the "Brown Earl") attempted to take control of his earldom, which had been disturbed since the death of his grandfather in 1326, he was supported by a now ailing King Robert Bruce of Scotland.
The Bruce invasion had a devastating effect on Ulster, and the earldom suffered a further blow in 1333 when the "Brown Earl" was assassinated by his own vassals. Thereafter, the earldom fell into the hands of absentees. It descended by marriage to Lionel of Clarence, and thence to the Mortimer earls of March.
Without the influence of a resident earl, the Gaelic Irish and mercenary Scots—notably the Clandeboye O’Neills and the Mac Donnells of the Glens of Antrim—encroached on the earldom, pushing the principal families into south County Down and the Ards peninsula. These families increasingly adopted Irish customs. We should, however, be careful not to exaggerate this development; it had begun long before 1333. Since de Courcy’s time, there had been veneration for Irish saints and alliances with native Ulster lords. At his death in 1326, the "Red Earl" was the subject of a Gaelic praise poem. Moreover, acculturation also moved in the other direction, as is shown by the appearance of the name "Henry" among the Ua Neills of Clandeboye. Nor in practical terms did English rule in Ulster end immediately with William de Burgh’s murder in 1333. It was a gradual process, and the earldom was still providing revenue, under its hereditary seneschals the Savages, in the 1350s. Moreover, for the rest of the medieval period, successive earls of Ulster—chosen for their connection with Ireland to serve as chief governor—attempted to regain the "bon-naght" of Ulster, which had been appropriated by the Ua Neills. The Gaelic chiefs repeatedly promised to render service. These promises were not made a reality, but this was in part due to chance rather than impotence. For instance, both the sixth (d. 1381) and eighth (d. 1425) Mortimer earls died within two years of their first successes in Ulster, with the result that the submissions they had taken could not be given practical effect.
In 1425, at the death of Edmund Mortimer, Ulster passed to Richard, duke of York. When the house of York came to the throne in 1461, Ulster became a permanent appanage of the English crown. Proposals for a reconquest appear in the accounts of the early Tudor period but were not implemented. Nonetheless, in 1541 when Conn Bacach Ua Neill suggested that he be made earl of Ulster, Henry VIII strongly rebuked him, reputedly calling Ulster one of the great earldoms of Christendom and an ornament of the crown. The Ua Neills were only made earls of Tyrone, and the royal claim to Ulster continued to be a factor in crown policy into the early modern period.