Kęstutis employed different military as well as diplomatic means in his struggle on the western borders of the Grand Duchy of Lithuania. In 1349, to avoid further clashes with the Teutonic Order, he started negotiations with Pope Clement VI for the Christianization of Lithuania, receiving promises for royal crowns for him and his sons. Algirdas willingly remained aside of the business and was concerned with the order in the Ruthenian part of the state. The intermediary in the negotiations, Polish King Casimir III, made an unexpected assault on Volhynia and Brest in October 1349 that ruined the Kęstutis's plan. During the Polish-Lithuanian war for Volhynia, King Louis I of Hungary made a peace agreement with Kęstutis on 15 August 1351, according to which Kęstutis obliged himself to accept Christianity and provide the Kingdom of Hungary with military aid, in exchange for the royal crown. The agreement was approved with a pagan ritual by Kęstutis to convince the other side. In fact, Kęstutis had no intentions to comply with the agreement and ran away on their road to Buda.