The Reformation swept through Europe during the 16th century. The excommunication of Protestants by leaders of the Roman Catholic Church ended centuries of unity among Western Christendom. The religion of an heir to the throne became an intensely important political issue. The refusal of Pope Clement VI to grant an annulment in the marriage of King Henry VIII to Catherine of Aragon saw Henry establish himself as supreme governor of the church in England. His female Protestant successors have served as Supreme Governor of the Church of England. Rivalry between Catholic and Protestant heirs ensued. Protestantism was consolidated in England by Henry's daughter, Elizabeth I, who influenced the development of Anglicanism through cultivation of an Elizabethan religious settlement with the publication of the "Book of Common Prayer". The religion of an heir or monarch's spouse complicated intermarriage between royal houses through coming centuries.