The Battle of the Yellow Ford was fought in County Armagh on 14 August 1598, during the Nine Years' War in Ireland. An English army of about 4,000, led by Henry Bagenal, was sent from the Pale to relieve the besieged Blackwater Fort. Marching from Armagh to the Blackwater, the column was routed by a Gaelic Irish army under Hugh O'Neill of Tyrone. O'Neill's forces divided the English column and a large earthwork stalled its advance. Bagenal was killed by an Irish musketeer, and scores of his men were killed and wounded when the English gunpowder wagon exploded. About 1,500 of the English army were killed and 300 deserted. After the battle, the Blackwater Fort surrendered to O'Neill. The battle marked an escalation in the war, as the English Crown greatly bolstered its military forces in Ireland, and many Irish lords who had been neutral joined O'Neill's alliance.

The Nine Years' War, sometimes called Tyrone's Rebellion, took place in Ireland from 1593 to 1603. It was fought between an Irish alliance—led mainly by Hugh O'Neill of Tyrone and Hugh Roe O'Donnell of Tyrconnell—against English rule in Ireland, and was a response to the ongoing Tudor conquest of Ireland. The war was fought in all parts of the country, but mainly in the northern province of Ulster. The Irish alliance won some important early victories, such as the Battle of Clontibret (1595) and the Battle of the Yellow Ford (1598), but the English won a decisive victory against the alliance and their Spanish allies in the siege of Kinsale (1601–02). The war ended with the Treaty of Mellifont (1603). Many of the defeated northern lords left Ireland to seek support for a new uprising in the Flight of the Earls (1607), never to return. This marked the end of Gaelic Ireland and led to the Plantation of Ulster.

The war against O'Neill and his allies was the largest conflict fought by England in the Elizabethan era. At the height of the conflict (1600–1601) more than 18,000 soldiers were fighting in the English army in Ireland. By contrast, the English army assisting the Dutch during the Eighty Years' War was never more than 12,000 strong at any one time.