The sixteenth and early seventeenth centuries in Ireland constitute one of the great watersheds in Irish history, a decisive period that witnessed the reduction of the whole island to effective English sovereignty. This conquest was not, however, the result of a consistent expansionist policy until the reign of Elizabeth, when an aggressive Dublin administration led by Sir Henry Sydney (1569–76) succeeded in establishing a militant programme that eventually tied successive administrations to extending English influence by forcible means into areas hitherto beyond the reach of crown government. Yet it was not until the end of Elizabeth's reign that the final contest for Irish sovereignty was fought. From 1594 until 1603, Hugh O'Neill, the Earl of Tyrone, led the last great Gaelic rebellion that shook the very foundations of English rule in Ireland and compelled the English government to commit financial resources that far exceeded the cost of military subvention in any of Elizabeth's continental wars.

The crushing success of English arms over rebel forces aided by Spain at the battle of Kinsale ultimately compelled O'Neill's unconditional submission to the Lord Deputy Mountjoy at Mellifont in county Louth on 30 March 1603 – six days after the death of Elizabeth. This military victory represented a necessary and primary phase in English domination over Ireland, but the second stage of political consolidation by judicial means was equally essential for England's lasting supremacy over the island.