The Nine Years' War or Tyrone's Rebellion took place in Ireland from 1594 to 1603. It was fought between the forces of Gaelic Irish chieftains Hugh O'Neill of Tír Eoghain, Hugh Roe O'Donnell of Tír Chonaill and their allies, against English rule in Ireland. The war was fought in all parts of the country, but mainly in the northern province of Ulster. It ended in defeat for the Irish chieftains, which led to their exile in the Flight of the Earls and 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.