Under constant pressure from the Guise and their allies, Henri III gave in and promulgated the Treaty of Nemours on 7 July 1585. This treaty demolished the peace that had been so patiently built by the various edicts of pacification, and went back on the policy of tolerance. The practice of the so-called Reformed faith was forbidden, and Protestants who did not renounce their religion faced exile. This Catholic reaction was further heightened by a papal bull dated 9 September 1585, which excommunicated Henri de Navarre and the prince de Condé and deprived them of their right to accede to the throne of France.
In such a context, Henri de Navarre announced the resumption of hostilities in a declaration on 30 November 1585. The eighth war confirmed his military prowess – on 20 October 1587 he crushed the duc de Joyeuse's royalist army at Coutras – and those of the duc de Guise, who won two battles against mercenaries associated with the Huguenots (at Vimory on 26 October and Auneau on 24 November). The duc de Guise's popularity among hard-line Catholics allowed him to impose his will, and he was carried away by the zeal and the violence of the Paris League that, on the Day of the Barricades on 12 May 1588, forced Henri III to flee to Chartres. On 15 July of that same year, the king signed the Edict of Union in which he pledged to root out heresy from the kingdom. A new States-General, held at Blois, forced the king to acknowledge the Edict as a fundamental and irrevocable law of the kingdom. Henri III slowly became convinced that only the elimination of the Guises would free him from their grasp. On 25 and 26 December 1588, he ordered the Forty-Five to assassinate the duc de Guise and his brother, the cardinal of Lorraine. This act radicalised the Paris League, culminating in the assassination of Henri III by a monk, Jacques Clément, on 1 August 1589.
When Henri de Navarre acceded to the throne, he inherited a kingdom in turmoil, the majority of whose subjects distrusted or outright rejected their new "heretic" king. The worst excesses took place in Paris where the Leaguers recognised the cardinal de Bourbon as "Charles X". On 15 November 1591, they lynched three members of the Parti des Politiques, including First President Barnabé Brisson, and two conseillers, Claude Larcher and Jean Tardif. The horrified reaction of the noble members of the League to these excesses was still not enough to allow Henri IV to quickly bring peace to France. Despite his conversion to Catholicism in 1593, his coronation in 1594 and the absolution declared by the pope in 1595, Henri's conquest and pacification of his kingdom took another three years, ending in the signing of the Edict of Nantes in 1598.