He tried to bring the kings of France and England to peace, but failed.
Made peace between Castile, Aragon, Navarre, Sicily, and Naples.
Worked to re-unite the Greek and Latin Churches.
Fought heresies, worked for monastic reform, and encouraged a new Crusade.
Condemned the propositions of John Wyclif and the Sachenspiegel in 1373.
Approved the Order of the Spanish Hermits of Saint Jerome in 1374.
Beginning in 1371 he became involved in conflict with Duke Bernabo Visconti of Milan, an enemy of the papacy.
Gregory was forced to declare war on Visconti in 1372 which lasted until a truce on 6 June1374.
However, Gregory's use of Frenchlegates in a dispute within Italy led to popular discontent.
The Pope excommunicated the inhabitants of Florence for rising against him.
The Florentines sent Saint Catherine of Siena to intercede for them.
Moved by the stength and insistence of her messages, he yielded, removed the excommunication, and moved the papal see back to Rome on 27 January1377.
However, popular uprisings against his use of temporal power continued, and he was on the verge of returning to France when he died.