War of the Three Henrys, (1587–89), the last of the Wars of Religion in France in the late 16th century, fought between the moderate but devious King Henry III, the ultra-Roman Catholic Henri I de Lorraine, 3e duc de Guise, and the Huguenot leader Henry of Bourbon, king of Navarre and heir presumptive to the French throne (the future Henry IV).
At first the balance of successes was somewhat in favour of the Holy League, the Catholic faction led by the Guises; but Henry of Navarre, with English financial aid, did win the Battle of Coutras (1587), in which the duc de Joyeuse, one of the favourites of Henry III, was defeated and killed. The duc de Guise, on the other hand, was too strong for the Protestant Germans, who had marched into France to join the Huguenots, and he defeated them at Vimory and Auneau, after which he marched in triumph to Paris, in spite of the orders and opposition of the king, who, finding himself powerless, withdrew to Chartres. Once more Henry III was obliged to accept such terms as the Leaguers chose to impose; and he signed the Edict of Union (1588), in which he named Guise lieutenant general of the kingdom and declared that no heretic could succeed to the throne. Unable to endure the humiliation, Henry III that same winter had the duke and the cardinal of Guise assassinated and many leaders of the League arrested. The power of the League party, however, seemed as great as ever; its new leader, the duc de Mayenne, entered Paris and declared open war on Henry III, who, after some hesitation, threw himself under the protection of his cousin Henry of Navarre in the spring of 1589. The Germans once more entered northeastern France; the Leaguers were unable to make headway either against them or against the armies of the two kings; they fell back on Paris, and the allies hemmed them in. All looked as if the royalists would soon reduce the last stronghold of the League, when Henry III was suddenly slain by a priestly assassin. Before he died the king had time only to commend Henry of Navarre to his courtiers as his heir and to exhort him to become a Catholic. Within a few years Henry of Navarre had allowed himself to be converted to Catholicism and had become the national sovereign as Henry IV.