In 1582 the United Provinces invited Francis, Duke of Anjou to lead them; but after a failed attempt to take Antwerp in 1583, the duke left the Netherlands again. After the assassination of William of Orange (10 July 1584), both Henry III of France and Elizabeth I of England declined the offer of sovereignty. However, the latter agreed to turn the United Provinces into a protectorate of England (Treaty of Nonsuch, 1585), and sent the Earl of Leicester as governor-general. This was unsuccessful and in 1588 the provinces became a confederacy. The Union of Utrecht is regarded as the foundation of the Republic of the Seven United Provinces, which was not recognized by the Spanish Empire until the Peace of Westphalia in 1648.