Immediately on his accession he attempted to reconcile the Kings of France and England, but failed. Gregory confirmed a
treaty between Sicily and Naples at
Villeneuve-lès-Avignon on 20 August 1372, which brought about a permanent settlement between the rival kingdoms, which were both papal fiefs. Gregory also tried to undertake a crusade due to pleas from
Catherine of Siena in 1376 by continuing Pope Urban V's call for Christians to stop fighting other Christians, which Urban called for in November 1366. Efforts were also made to reform corrupt practices in the various monastic orders, such as collecting fees from persons visiting holy sites and the exhibiting of faux relics of saints. Before moving to Rome, however, he had to give his entire attention to the turbulent affairs of Italy. Duke
Bernabo Visconti of Milan, had, in 1371, made himself master of Reggio and other places that were feudatory to the Holy See. Gregory XI excommunicated him and later declared war on him in 1372 against a Florentine led coalition of Italian city states, which later became known as the
War of the Eight Saints (1375–1378). After war broke out, Gregory excommunicated the city and placed the city under interdict on 31 March 1376 in an attempt to quell the rebellion. Catherine of Siena tried to convince Gregory to stop the war on behalf of the Florentine state. Gregory was constantly receiving pleas from
Catherine of Siena through letters. In total, she wrote 14 letters between 1375 and 1378 until Gregory died. These letters dealt with different matters such as peace, church reform, and moving the papacy back to Rome. Catherine persuaded him by saying that it was easier to achieve Gregory's goal of peace among the city states in Italy by expanding the influence of the Papal states if the papacy were back in Rome. ==Death==