Pope Paul IV, born Gian Pietro Carafa, was head of the Catholic Church and ruler of the Papal States from 23 May 1555 to his death, in August 1559. While serving as papal nuncio in Spain, he developed an anti-Spanish outlook that later coloured his papacy. In response to an invasion of part of the Papal States by Spain during his papacy, he called for a French military intervention. After a defeat of the French and with Spanish troops at the edge of Rome, the Papacy and Spain reached a compromise: French and Spanish forces left the Papal States and the Pope thereafter adopted a neutral stance between France and Spain.

The Papal States, officially the State of the Church, were a conglomeration of territories on the Apennine Peninsula under the direct sovereign rule of the Pope from 756 until 1870. They were among the major states of Italy from the 8th century until the Unification of Italy, between 1859 and 1870.