Philippe Emmanuel de Lorraine (1558–1602), Duke of Mercœur, whom Henry III had made governor of Brittany in 1582, was endeavouring to make himself independent in that province. In 1590, Mercœur rebelled against the ascension to the throne of France of Henry of Navarre and becomes the head of the Catholic League of Brittany, aiming to return to restore the autonomy of the former Duchy, and proclaimed protector of the Catholic Church in the region of Brittany. He also invoked the hereditary rights of his wife, Marie de Luxembourg, who was a descendant of the dukes of Brittany and heiress of the Blois-Brosse claim to the duchy as well as Duchess of Penthièvre in Brittany, and organized a government at Nantes. Proclaiming his son "prince and duke of Brittany", he allied with Philip II of Spain.
With the aid of the Spanish, Mercœur defeated Henry IV's forces under the Duke of Montpensier, at Craon in 1592, but the royal troops, reinforced by English contingents [headed by Sir John Norreys], soon recovered the advantage.