The Holy League of 1571 was arranged by Pope Pius V and included the major Catholic powers of southern Europe, specifically the Spanish Empire as well as the Italian maritime powers. It was intended to break the Ottoman Empire’s control of the eastern Mediterranean Sea and was formally concluded on 25 May 1571. Its members were:the Papal States under Pius V, Spanish Empire under Philip II, the Republic of Venice, the Republic of Genoa, the Knights of Malta, the Grand Duchy of Tuscany and the Order of Saint Stephen under Cosimo I de' Medici, the Duchy of Savoy under Emmanuel Philibert, the Duchy of Urbino under Guidobaldo II della Rovere, the Duchy of Parma under Ottavio Farnese.

Pope Pius V, OP, born Antonio Ghislieri, was head of the Catholic Church and ruler of the Papal States from 7 January 1566 to his death, in May 1572. He is venerated as a saint of the Catholic Church. He is chiefly notable for his role in the Council of Trent, the Counter-Reformation, and the standardization of the Roman Rite within the Latin Church, known as Tridentine mass. Pius V declared Thomas Aquinas a Doctor of the Church.