The War of the Three Henrys took place during 1585–1589, and was the eighth conflict in the series of civil wars in France known as the French Wars of Religion. It was a three-way war fought between:

• King Henry III of France, supported by the royalists and the politiques;
• King Henry of Navarre, later Henry IV of France, heir presumptive to the French throne and leader of the Huguenots, supported by Elizabeth I of England and the Ge, rman protestant princes; and
• Henry of Lorraine, Duke of Guise, leader of the Catholic League, funded and supported by Philip II of Spain.

The underlying cause of the war was the looming royal succession crisis from the death of heir presumptive, Francis, Duke of Anjou (Henry III's brother), on 10 June 1584, which made the Protestant Henry of Navarre heir to the throne of the childless Henry III, whose death would extinguish the House of Valois. On 31 December 1584, the Catholic League allied itself with Philip II of Spain by the Treaty of Joinville. Philip wanted to keep his enemy, France, from interfering with the Spanish army in the Netherlands and his planned invasion of England.

The war began when the Catholic League convinced (or forced) King Henry III to issue the Treaty of Nemours (7 July 1585), an edict outlawing Protestantism and annulling Henry of Navarre's right to the throne. Henry III was possibly influenced by the royal favorite, Anne de Joyeuse. In September 1585, Pope Sixtus V excommunicated both Henry of Navarre and his cousin and leading general Condé to remove them from the royal succession.