English government in Ulster in the early 1590s has taken the form of a Provincial Presidency, headed by the colonist Sir Henry Bagenal who lives at Newry.

O'Neill had roused the ire of Bagenal in 1591 by eloping with his sister, Mabel, but in 1593 had showed his loyalty to the crown with his military support for his brother-in-law in the defeat of Hugh Maguire at Belleek.

After Mabel's death, O'Neill had gradually fallen into a barely concealed opposition to the crown and sought aid from Spain and Scotland.

The Nine Years War begins with a conflict over English efforts to maintain a string of garrisons along the southern border of Tyrone's territory in Ulster.

The Irish leader promptly besieges the English garrison at Monaghan castle, and Bagenal marches out to its relief on May 25 (June 4 New Style) from Dundalk, via Newry.

His army is made up of seventeen hundred and fifty troops, including some veterans and certain companies newly arrived from the Spanish campaign in Brittany, but there are many recruits in the ranks.

Bagenal's men are predominantly infantry, armed with muskets and pikes; there is also a small number of horsemen raised in the Pale.

The Battle of Clontibret is essentially a two day running fight, as Bagenal's column is ambushed on its way to and from Monaghan town.

It ends in victory for Tyrone, and is the first severe setback suffered by the English during the war.

The English authorities in Dublin Castle have been slow to comprehend the depth of Tyrone’s rebellion.

English armies after failed negotiations in 1596 had tried to break into Ulster but had been repulsed by a trained army including musketeers in prepared positions.

Up to two thousand English troops are killed on August 14, 1598, at the Battle of the Yellow Ford, after being ambushed on the march to Armagh.

The rest are surrounded in Armagh itself but negotiate safe passage for themselves in return for evacuating the town.

Ó Neill's personal enemy, Henry Bagenal, had been in command of the army and had been killed during the early engagements.

It is up to this point the heaviest defeat ever suffered by the English army in Ireland.