Henry VIII died in 1547 and was succeeded by Edward VI who was the son of Henry's third wife, Jane Seymour. Edward died in 1553 and was succeeded by Mary, the only one of the six children of Henry VIII and Catherine of Aragon who survived.

Mary, a Catholic, married Philip II of Spain. She repealed the laws establishing Protestantism in England and re-established Roman Catholicism. Often referred to as "Bloody Mary" she is noted for her persecution of Protestants. She dealt equally harshly with the Irish. She confiscated lands belonging to the O'Moores and the O'Connors in counties Laois and Offaly, renaming them Queen's County and King's County in honour of herself and her husband. The dispossessed chieftains waged a guerrilla war against the English settlements. Under the pretext of holding a peace conference with them, the English invited the O'Moores and the O'Connors to Mullaghmast where they had them and their families treacherously murdered.