Historians, How did Brian Boru rise to power in 1002?

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The End of Uí Néill Hegemony

Before Brian Boru's rise to power, Ireland was dominated by the Uí Néill, who were divided into two main septs; one in Ulster and one in Mide. These septs shared a single throne, and alternated upon the death of a ruler. Through a series of unfortunate events in the early 10th century, beginning with the death of Niall Glúndub in 919 and later his son and the prospective king from Southern Uí Néill, the kingdom of the Uí Néill was left with no clear successor. Two claimants in the north and south, both from lineages which had been excluded from succession for centuries, waged a civil war until one of them, named Congalach won. He attempted to assert his hegemony across Ireland, but had another rival named Domnall who claimed the throne after Congalach was killed in an ambush by Norse and Irish forces in Leinster.

Medieval Ireland was never a peaceful place, and small-scale warfare was pretty common, but as you can see the hegemony of the Uí Néill had been broken by dynastic strife; while their kingdom as a whole managed to subjugate a good chunk of the island, in this period those campaigns were often led by rival claimants to the throne, which made their internal stability even worse. By the 970s, a particularly brutal dynastic struggle gripped Domnall's kingdom, and he marched into Mide and scourged the countryside. When he died in 980, it might have appeared that things were looking up for the Uí Néill, as his strategy did manage to end dynastic strife within the kingdom, but the long-term effects of this half-century of conflict were coming home to roost.

During this long period of dynastic struggles for the kingship of the Uí Néill, the provincial kings of Munster, Leinster and Connacht had the opportunity to build up their strength without interference from the once-dominant Uí Néill, whose power had once been so great that the kingship of the Uí Néill was synonymous with the kingship of Ireland. But what does this have to do with Brian Boru, you might ask?

The Rise of Brian Boru

During this period, a significant political change had occurred in Munster as well. The Eóganachta, the Kings of Cashel who had ruled the province since the 5th century, had been considerably weakened by their northern neighbours and Viking raids. The Dál gCais of modern County Clare had managed to take the kingship of Munster by force from the Eóganachta while their Uí Néill overlords were preoccupied with fighting amongst themselves.

Brian Boru was the brother of the Dál gCais king who had claimed the kingdom of Munster, and spent many of his early years building his reputation and honing his military skills by leading a small band of warriors in the wilderness of Co. Clare, establishing forts and allegedly waging a sort of guerrilla warfare against raiding vikings. Upon the death of his brother, he ascended to the throne of Munster and waged some small wars to avenge the death of his brother. He spent some time building up his power, before waging some wars of subjugation against smaller, neighbouring kingdoms. His campaign against Osraige to the east brought him into conflict against the new and capable Uí Néill king, Máel Sechnaill, who had just broken the power of the Scandinavian kingdom of the Isles in Ireland.

Brian managed to subjugate Osraige after capturing their king in battle, but suffered several defeats at the hands of Máel Sechnaill. Later, he set out to extend his overlordship over the province of Leinster, and enlisted the aid of nearby Scandinavian settlements in Waterford who attacked by sea as Brian's forces marched overland. After defeating a revolt in Munster, he spent some time consolidating his rule in that province before launching a raid against Máel Sechnaill's territory in Mide, and sent another detachment to the province of Connacht which was quickly routed. The two kings were at war periodically for the next few decades, and both sent raiding forces into the other's territory, which Brian responded to by fortifying some key areas.

In 997, Brian was the de facto ruler of Ireland's southern half, having consolidated his rule in Munster and having subjugated the province of Leinster. This fact was formally recognized by Máel Sechnaill in the same year and the two agreed on their respective overlordship of each half of the island and sent each other hostages. The two kings of Ireland then launched a collaborative mission against the Scandinavian kingdom of Dublin.

Brian Boru - Overlord of Ireland

In 999, one year before the new millennium, the men of Leinster who had been subjugated by Brian rose up in rebellion, allied with the Norsemen of Dublin. He quickly crushed this rebellion and then decided to go back on his agreement with his Máel Sechnaill, and mustered a huge army (relatively speaking) drawn from all of southern Ireland and led it against the Uí Néill king, but withdrew after suffering a minor defeat. In a later conflict, Brian managed to defeat the king of the north and took hostages from him, which in medieval Ireland signified one king's overlordship over another.

What this means is that Brian was now overlord (but not king) over almost all of Ireland, with only a few kingdoms remaining independent in the furthest north of Ulster. With Máel Sechnaill, now his subject, at his side, he marched to the north in an attempt to gain their submission and succeeded after a few cautious, probing attacks. This campaign lasted about 6 years, and by the end of it he could have legitimately claimed to be a High-King of Ireland, having subjugated the kings of the entire island.

The last few years of Brian's rule were mostly concerned with ecclesiastical politics, until a major rebellion broke out as Leinster, allied with Norse Dublin, rose up once more. This time, Dublin's king had arranged for the support of many Scandinavian warriors from across the British Isles, and assembled a large force of Scandinavians and Leinstermen at Clontarf, outside Dublin. Boru's forces managed to defeat the rebels, however in the aftermath of the battle, a band of retreating Norsemen came across the king, now an old man, who was supposedly praying for victory in his tent and slew him. According to Njal's Saga, Bróðir, the warrior responsible for Brian's death, was bound to a tree and had his entrails spun around it. It's more likely that he was simply killed while fleeing the battle, but that doesn't make a nice revenge story, does it?

The Legacy of Brian Boru

Although Brian Boru might have been able to call himself King of Ireland, the nature of overlordship in medieval Ireland meant that his rule was never as consolidated as a national monarch in France or England; other kings simply recognized that he was their overlord and gave him hostages and some troops, but still maintained a large degree of independence. Before Brian, the idea of a High-Kingship was mostly a poetic and symbolic title, but he had established the precedence of a single king ruling the entire island. Later on, Brian would be described in the Book of Armagh as Imperator Scottorum (Emperor of the Irish), rather than the traditional Ard ri (High-King), which implies that his hegemony over Ireland was more real than previous kings. While Brian never established a national monarchy, Irish history from his death until the coming of the Normans was the history of provincial kings making war on one another in an attempt to have themselves proclaimed as a High-King like Brian Boru. His impact on Irish history was thus more related to his legacy and the precedence that he established than his actual reign; after his death, the idea of a High-King ruling all of Ireland was projected onto the past by the 'men of art' who produced Ireland's historical and genealogical texts. That Irish legal texts, infamous for their categorization of everything imaginable, do not ever mention a 'High-King' alongside other categories of kings tells us that such an office never existed before the perception of its possibility to be realized was created by Brian.