The Williamite War in Ireland was a conflict between Jacobites (supporters of Catholic King James II) and Williamites (supporters of Protestant Prince William of Orange) over who would be King of England, Scotland and Ireland. It is also called the Jacobite War in Ireland or the Williamite–Jacobite War in Ireland.
The cause of the war was the deposition of James II as King of the Three Kingdoms in the "Glorious Revolution" of 1688. James was supported by the mostly Catholic "Jacobites" in Ireland and hoped to use the country as a base to regain his Three Kingdoms. He was given military support by France to this end. For this reason, the War became part of a wider European conflict known as the Nine Years' War (or War of the Grand Alliance). Some Protestants of the established Church in Ireland also fought on the side of King James.
James was opposed in Ireland by the mostly Protestant "Williamites", who were concentrated in the north of the country. William landed a multi-national force in Ireland, composed of English, Scottish, Dutch, Danish and other troops, to put down Jacobite resistance. James left Ireland after a reverse at the Battle of the Boyne in 1690 and the Irish Jacobites were finally defeated after the Battle of Aughrim in 1691.
William defeated Jacobitism in Ireland and subsequent Jacobite risings were confined to Scotland and England. However, the War was to have a lasting effect on Ireland, confirming British and Protestant rule over the country for over a century. The iconic Williamite victories of the Siege of Derry and the Battle of the Boyne are still celebrated by the (mostly Protestant) Unionist community in Northern Ireland today.