Conference of bishops .|alt=A color portrait of a middle-aged man in black regal costume By late 1592 the Crown's continual advances into Ireland, as well as the recent executions of chieftains
Hugh Roe MacMahon in 1590 and
Brian O'Rourke in 1591 had created a fierce resentment in the Gaelic nobility and Irish Catholic clergy. Catholic priests were suffering harassment and imprisonment from English authorities, and
Spain had been a refuge to the Irish Catholic clergy since the 1570s. Archbishop
Edmund MacGauran returned from Spain with promises from
King Philip II to support oppressed Irish Catholics if they proved themselves by launching prior military action. In December, a conference of seven northern bishops met in Tyrconnell. O'Donnell pledged his support to the Irish Catholic cause, and as a leading force of the emerging confederacy he began to work with MacGauran to secure Spanish support. On 29 March 1593, O'Donnell wrote to Irish nobles living in Spain, saying they could not hold out for long against the Crown without Philip II's backing.
Maguire's revolt Humphrey Willis was appointed by FitzWilliam as Sheriff of Fermanagh against Maguire's will. In early April 1593, Willis entered Fermanagh with at least 100 men and began violently raiding. This exacerbated resentment towards the Crown, and after Willis' first offensive, O'Donnell met with MacGauran, Maguire,
Brian Oge O'Rourke and
Theobald, Richard and John Bourke at
Enniskillen Castle on 28 April. MacGauran advised the noblemen to sign a letter to Philip II which emphasised their oppression and requested urgent reinforcements from the
Spanish army. The
Archbishop of Tuam,
James O'Hely, was tasked with delivering the confederates' messages: two letters from O'Donnell, one letter from MacGauran, and the 28 April letter signed by the confederates. Maguire obtained reinforcements from Tyrone's brother and foster-brothers, who were likely involved on Tyrone's behalf, and forced Willis and his men from Fermanagh. Maguire's revolt marked the start of the
Nine Years' War.'s stronghold,
Enniskillen Castle.|alt=A color photograph of one side of a castle wall painted greyHistorians have debated O'Donnell's position within the confederacy. Historians
Nicholas Canny, Michael Finnegan, John J. Silke and Darren McGettigan credit O'Donnell as the confederacy's driving force until Tyrone's break into open rebellion. Historians
Hiram Morgan and James O'Neill have disputed this by emphasising that Tyrone was a more important figure who hid his allegiance to the confederacy for strategic reasons. The
Sheriff of Monaghan alleged Tyrone had attended the meeting at
Enniskillen Castle, though Tyrone did not sign MacGauran's letter. Around August 1593, Maguire stated to a spy that Tyrone had pushed him into rebellion and "promised to assist him and bear him out in his war". Many of Tyrone's British contemporaries, such as Perrot and
Geoffrey Fenton, considered O'Donnell to be the junior partner in the confederacy. O'Hely reached the Spanish court by September 1593, where he met with royal secretary
Juan de Idiáquez. In Idiáquez's notes to Philip II, he notes the early confederates wanted Tyrone to join them in open rebellion, though it appears Tyrone refused to publicly defy the Crown without reassurances on the arrival of Spanish reinforcements.
Secret rebellion Catholic bishops spread the Aodh Eangach prophecy to advance the Irish rebellion. Maguire and O'Rourke continued to rebel by attacking English forces. O'Donnell aided the growing rebellion by sending MacSweeney
gallowglass, but publicly he feigned neutrality. He lacked sufficient forces to combat a direct assault from English forces; he also faced pressure from his father-in-law to likewise appear publicly loyal to the Crown. O'Donnell used the chiefdoms of Maguire and O'Rourke as a buffer against Bingham's forces. He also advised Maguire and sheltered his creaghts on Tyrconnell's borders. MacGauran was killed on 23 June 1593 whilst accompanying Maguire on a raid. In September, O'Donnell sent his mother to Scotland to secure further Scottish troops. Maguire's rebellious activity provoked a large-scale military expedition led by Marshal
Henry Bagenal which culminated at the
Battle of Belleek in October. Tyrone fought on Bagenal's side ostensibly to prove his loyalty to the Crown. O'Donnell was in nearby
Ballyshannon when the battle was taking place, but he was ordered by Tyrone not to reinforce Maguire. The battle was a ploy to make the confederacy seem weaker than it actually was, thus diverting English attention away from Ireland. O'Donnell partially disobeyed Tyrone's order and sent 60 horsemen, 60 swordsmen and 100 gallowglass under the command of Niall Garbh. Historian James O'Neill argues O'Donnell intentionally dispatched the antagonistic Niall Garbh to
Belleek hoping he would die in the slaughter. Bagenal's forces won the battle. Despite the successful ploy, the battle was damaging to O'Donnell. Many of the gallowglass were killed and Niall Garbh survived. To placate the Crown's victorious army, O'Donnell sent 115 cattle to the English camp as a gift. A letter from O'Donnell was later found on the corpse of a Redshank captain killed in the battle. By November 1593, Bingham was aware O'Donnell was secretly assisting Maguire and O'Rourke. The Crown demanded Tyrone bring O'Donnell under control, and in March 1594, the two men met with government commissioners near Dundalk. O'Donnell professed "his ancestors had always been loyal to her majesty, and so he would continue but stood in danger of his life and feared practices would be used against him". Tyrone submitted a list of his and O'Donnell's grievances, but the talks ended in confusion when O'Donnell threatened to kill some of Tyrone's English friends. Afterwards government commissioners surmised a confederacy had been established between the Ulster lords. In March 1594, Philip II sent a Spanish ship—containing O'Hely, Spanish experts and Irish émigrés—to Ireland on a reconnaissance mission, but the crew died when it was shipwrecked off the coast of
Santander.
Open rebellion served as Lord Deputy from 1594 to 1597.|alt=A color portrait of a burly man in English aristocratic costume O'Donnell was aware Tyrconnell would become an easy target if Maguire and O'Rourke's territories were occupied by the English. In February 1594, he demolished castles in Belleek and Bundrowes to prevent English forces from taking them, and he concentrated his forces at Ballyshannon on his mother's advice. That same month, Captain John Dowdall captured Enniskillen Castle, Maguire's stronghold, after a
nine-day siege. O'Donnell rushed to Maguire's aid, assembling an army and joining Maguire to retake the castle. He stated he "would not leave that siege until he had eaten the last cow in his country". The castle was blockaded by 11 June, and by late July the English soldiers were suffering from food shortages. O'Donnell's decision to join the siege of Enniskillen brought his rebellion into the open. O'Donnell encountered resistance from his family, with both his brother Rory and his father Hugh McManus opposing his choice to go to war. Frustrated with Tyrone's
loyalist facade, O'Donnell warned him that "he must consider Tyrone his enemy, unless he came to his aid in such a pinch". Tyrone subsequently sent reinforcements under his brother
Cormac MacBaron O'Neill to the
Battle of the Ford of the Biscuits. O'Donnell continued to negotiate through his father-in-law; in August, Tyrone presented the new Lord Deputy,
William Russell, with a lengthy document of O'Donnell's grievances and demands. O'Donnell requested a general pardon for himself and his followers, as well as clemency for Maguire, O'Rourke and rebels in
County Monaghan. Russell ignored these demands and resupplied Enniskillen castle with 1,200
Irish Army soldiers, comprising most of the troops at his disposal. The English relief mission was successful but ominously peaceful—Russell lost communication with his spies as they had all been captured by confederate soldiers. By early 1595, Tyrone had finally joined O'Donnell in open rebellion with an
assault on the Blackwater Fort.
Expansion into Connacht , Lord President of Connacht, who had persecuted Connacht's Gaelic population.|alt=A color portrait of a young man in English aristocratic costume In 1595, O'Donnell began to expand his rebellion into Connacht. His ancestors, particularly his grandfather
Manus O'Donnell, had ruled over Lower Connacht, and Hugh Roe O'Donnell increasingly demanded the restoration of these lands. Richard Bingham had persecuted Connacht's Gaelic population since the mid-1580s, causing many refugees to flee to Tyrconnell. O'Donnell aided the refugees and recruited many of them as swordsmen. O'Donnell resented Bingham and was "easily tempted" by the refugees, who urged him to attack Bingham's administration. O'Donnell invaded Connacht on 3 March 1595 with 400 men. From
Rathcroghan, the province's ancient royal capital, he launched large raids into
Longford and
Roscommon. In June 1595, the castle of
Sligo, which was key to securing control over the province, was betrayed to O'Donnell "in a stroke of luck"; Bingham's government collapsed. O'Donnell reestablished
Brehon law and asserted suzerainty over north Connacht. By 1595, O'Donnell and his wife were facing difficulties; Rose had not borne him children. In order to increase his influence in southern Connacht, O'Donnell had hopes of a marriage alliance with Lady Margaret Burke, daughter of the neutral
3rd Earl of Clanricarde. With Tyrone's consent, Rose and O'Donnell separated. However, the government became aware of his plan to reportedly take Margaret from her parents by surprise or force, and in December she was placed in protective custody. Additionally Clanricarde stated he would "rather see [Margaret's] burial than her marriage to [O'Donnell] were he a good subject". Tyrone sent his trusted secretary
Henry Hovenden to Tyrconnell to advise O'Donnell, and O'Donnell eventually took Rose back. His choice to remain in a marriage with no children is representative of his dependence on Tyrone. == Peace talks ==