To fully understand the importance of the role played by Somhairle Buidhe Mac Domhnaill in the early English failures of plantation in Ulster, one must appreciate the threat posed to the English crown by his background and lineage. Somhairle Buidhe Mac Domhnaill, which translates as Somerled of the yellow hair, son of Donell, more commonly known by his Anglicized name, Sorley Boy MacDonnell, was the son of Cather Maclan and Alexander MacDonald of Dunyvaig and the Glens in Antrim, who in turn were descended from King John of the Isles. During Somhairle’s youth, Alexander established a power base for his family in both Ulster and Scotland. Because of this, Somhairle was seen as a Scottish-Irish fliath, a term used for any person belonging to a powerful family but who is not necessarily, as it often is presumed, a chief. However, Somhairle, his father, and brother each were, in fact, chiefs of the MacDonald clan. This essay will outline the series of events that demonstrate how Somhairle’s connections with both Scottish and Irish clans became to be viewed by the English as a threat to early English attempts at plantation in Ulster.
Between 1562 and 1569 the clans O’Neill and Mac Donald were engaged in open feud. In 1562 Elizabeth I recognized Shane O’Neill as head of the O’Neill’s, but by 1563, Thomas Radclyffe, the third Earl of Sussex, had begun a campaign to weaken the power of the O’Neill’s in Ireland, a campaign that the MacDonald’s were heavily involved in. Sussex eventually gave up his campaign against the O’Neill clan, but O’Neill did not forget the MacDonald involvement and launched a full attack on the clan, apparently with the aim of ridding Ireland of further Scottish interference. Somhairle Buidhe and the Mac Donald’s were defeated in battle by the O’Neill’s in 1564 near Coleraine. In 1565 O’Neill, taking advantage of the weakened state of the MacDonald’s, attacked the Glens, which is where the MacDonald clan was situated, and defeated the MacDonald’s at the Battle of Glentasie. There O’Neill took Somhairle Buidhe and his brother James, the chief of the Mac Donalds, as captives. James eventually died of his wounds in captivity but Somhairle survived and by 1567 had, it would seem, gained the confidence of his captures as O’Neill turned to the Mac Donald’s of Antrim for Scottish reinforcements following an unexpected defeat at the hands of the O’Donnell’s. Somhairle Buidhe then organized a feast, through his younger brother, at Cushendun in north Antrim. An argument broke out at the feast, which ultimately ended with the murder of Shane O’Neill. In 1569 however, an alliance was established between the two clans with the marriage of Turlough Luineach O’Neill, Shane’s successor, and Agnes, the widow of James Mac Donald, Somhairle Buidhe’s late brother. The new couple was married on Rathlin Island. But, more importantly, this new alliance between two of the most powerful clans in Gaelic Ireland did not go unnoticed by the English.
Having reached an alliance with the O’Neill’s, an alliance that posed a strong Gaelic defence against any English power or attempts at control in Ulster. Somhairle Buidhe now turned his attention to the work of Sir Thomas Smith, who was attempting to plant English settlers in Ulster. Somhairle Buidhe brought Scottish reinforcements to Ireland where he attacked Carrickfergus in 1572. Somhairles Scottish alliance was also keenly observed by the English, as a Gaelic Irish alliance was one thing but a Scottish/Irish alliance could lead to similar rebellious behavior in the Scottish highlands. The fact that Scottish reinforcements were sent to Ireland in order to fight along side the Gaelic Irish against the English power demonstrates how the Gaelic sphere in both Scotland and Ireland can possibly be seen as a united front. Somhairle was wounded in the failed attack and so tried petitioning Elizabeth for legal recognition. Somhairle was successful in this endeavor, and on the 14 April 1573 he was offered a patent of denization. This patent gave him certain rights of possession that were usually only given to subjects of the English crown, on the condition that he offer support to the crown should anyone threaten or oppose English influence in Ulster. However, this arrangement did not last as Elizabeth’s advisors convinced her that an English plantation was the best way in which to control Ulster. Walter Devereux, the first Earl of Essex, was sent to Ulster along with 400 other colonists with the titles for land in Clandeboye, Rathlin Island, the Route, and the Glens. Having joined forces with Smith, Essex, following some failed attempts at negotiations, seized the lands and killed Sir Brian Mac Phelim O’Neill of Clandeboye and the chief of the MacQuillan clan.  This left Somhairle Buidhe as the last remaining supplier of redshanks, soldiers from western Scotland, to the Gaelic clans in Ulster. This meant Somhairle Buidhe and his clan posed the final threat to English power in Ulster and, which prompted Elizabeth’s decision to remove all the MacDonalds from Ulster.
On the 27 July 1575, Turlough Luineach finally submitted to a peace agreement with Essex. Having won a battle against Somhairle Buidhe near Toome earlier that month, Essex ordered a naval attack led by John Norris on Rathlin Island. Somhairle Buidhe and his supporters had sent their women, children, elderly and infirm to Rathlin Island, off the coast of Antrim, for protection. The Scots and Irish used Rathlin Island as a sanctuary due to its natural defenses of rocky shores, but also because it was respected as a place of refuge, having been associated historically with St. Columba. Norris easily took the castle that the inhabitants of the island had retreated to. He placed the castle under siege for two days after which it was forced to surrender. The inhabitants of the castle, except for the Constable and his family, were all slaughtered. Norris’s forces proceeded to murder between 500 and 600 women and children that were hiding in the caves on the island. While Norris had been ordered with taking the island, Sir Francis Drake was given the task of preventing any Gaelic Irish or Scottish reinforcements reaching the island and so Somhairle Buidhe was forced to stay on the mainland and as Essex wrote in his letter to Elizabeth’s secretary following the attack “was likely to have run mad for sorrow, tearing and tormenting himself and saying that he there lost all that he ever had.” 
Even after this massacre, Somhairle Buidhe continued to be a threat to English power in Ulster, for he took revenge through a successful raid on Carrickfergus, and managed for some time to reclaim his power and authority in the Glens. Somhairle Buidhe continued to attack the English from both Ireland and Scotland until he finally submitted once he received a grant to a large portion of the Route country for himself and his heirs, as well as being made constable of Dunluce Castle. He died in 1590, at the age of 85, in the castle in Dunanynie where he was born, and received the traditional burial of a MacDonald chief at Bonamargy Friary, Ballycastle. Somhairle Buidhe as a Gaelic chief was not exceptional, for many clan chiefs at the time similarly opposed English power in any way they could. However it was his impressive networking skills that allowed him to create strong and powerful alliances with both Gaelic Irish clans, such as the O’Neills, as well as Scottish clans, that increased his power and therefore his threat to the English.
 Hector McDonell, ‘’MacDonnell, Sorley Boy (b. in or before 1508, d. 1590)’, Oxford Dictionary of National Biography, Oxford University Press, 2004; online edn, Jan 2008 [http://www.oxforddnb.com/view/article/17465
 McDonnell ‘MacDonnell, Sorley Boy (b. in or before 1508, d. 1590).’
 Caoimhín Breatnach, “The Murder of Shane O’Neill: Oidheadh Chuinn Chéadchathaigh,” Ériu 43 (1992): 159–175.
 McDonnell, ‘MacDonnell, Sorley Boy (b. in or before 1508, d. 1590).’
 McDonnell, ‘MacDonnell, Sorley Boy (b. in or before 1508, d. 1590).’
 Hugh Forde, Sketches Of Olden Days In Northern Ireland: Including Portrush, Dunluce Castle, Dunseverick Castle ... (Belfast, 1923).
 McDonnell, Hector, ‘MacDonnell, Sorley Boy (b. in or before 1508, d. 1590).’