Boyne, Battle of the, July, 1690, a battle between the Protestant forces of William III, king of England, and the Catholic forces of the deposed James II. It was fought in the valley of the River Boyne near Drogheda in northeastern Ireland. Eighteen months before, in the “Glorious Revolution” of 1688, James had been driven from the English throne and replaced by his sister Mary and her husband, William of Orange, who ruled jointly. James then went to Ireland, where he had many supporters and where he was aided by Louis XIV of France, then at war with England. King William crossed to Ireland and defeated James. The movement to restore James to the throne continued for some time, but the Battle of the Boyne greatly strengthened William's position.