The Treaty of Joinville (31 December 1584) was an agreement between Philip II of Spain and the more radical French Catholics, led by Henry, duke of Guise, aimed at preventing the Protestant Henry of Navarre coming to the French throne.
On 10 June 1584 Francois, duc d’Anjou, the younger brother and heir of Henry III, died, leaving Navarre as the heir to the French throne. This was unacceptable to Guise and his supporters, and to Philip II (who also had an interest in keeping France unsettled). Philip was willing to support the Catholic side in the ongoing French civil wars, and sent an envoy to Guise's castle at Joinville to negotiate a treaty.
Philip II was represented by Juan Baptista de Tassis, until recently the Spanish ambassador to the French court, and Juan Moreo, commander of the Knights Hospitallers of Malta.
The French Catholics were represented by Henry, duke of Guise and Charles, duke of Mayenne. Guise also represented his brother, Cardinal Louis of Guise and his cousins, Charles, Duke of Aumale and Charles de Lorraine, duke of Elbeuf
Finally the Catholics had their own candidate for the throne, Cardinal Charles of Bourbon, who was represented by Francois de Bourbon.
The most important clauses of the treaty saw both sides recognise the Cardinal of Bourbon as heir to the French throne, excluding all heretical claimants. The League agreed to eliminate Protestantism in France. In return Philip II promised to pay the League 50,000 gold crowns per month, although this was a loan to be repaid by the Cardinal after he came to the throne.
The Cardinal was also to ratify the treaty of Cateau Cambrésis, which had ended the Fifth Hapsburg-Valois War (1551-59), agree to an eternal alliance with Philip II and his successors, not to interfere in any way with the Spanish trade with the Indies and to accept the decrees of the Council of Trent.
The Treaty of Joinville was a key step towards the outbreak of the Eighth War of Religion (1585-1589), or the War of the Three Henries, the start of 15 years of civil war in France. Guise’s Catholic League soon gained control of large parts of France, and eventually Henry III was forced to come to terms with the League, siding against the Huguenots.