After this treaty was signed, Murad withdrew to Brusa in order to provide for the organization of the new possessions that had come to him by a successful expedition against Angora. His letters, written at this time to announce to his Anatolian neighbours and to the Moslem princes of Asia the victories in Thrace, show clearly that he did not yet feel himself strong enough to assume the position of overlord to the other great emirs of Asia Minor. While he was in Brusa, in the spring of 1363, an event happened which led Murad to make the momentous decision that shaped the destinies of the Ottoman Empire. The first coalition against the Osmanlis was formed in Europe. IV After the fall of Philippopolis, the Greek commandant had succeeded in escaping, and took refuge with Kral Urosh V of Serbia.[269] He pointed out to Urosh most eloquently the paucity of numbers of the Osmanlis, their insecure position, and the danger that would overwhelm the Serbians if they waited until the Osmanlis were firmly grounded in Thrace. Urged by Pope Urban V, the princes of Wallachia and Bosnia, together with King Louis of Hungary, joined the Serbians in upper Macedonia. Under the guidance of the Greek refugee, they started on a swift march to win back Adrianople. It was an expedition undertaken as a crusade. The allies mustered at least twenty thousand. Lalashahin had hardly more than twelve thousand men under his command, and a portion of these were scattered in the captured cities. Murad, who had started to return to Thrace as soon as he had heard the news, was detained by the necessity of capturing a fortress on the Sea of Marmora, near Cyzicus, which was in the hands of a turbulent band of second-generation Catalans, whom he feared to leave behind him.[270] They were suspected of plotting with his southern rivals to organize a movement against his Anatolian possessions. If the Greeks had had the power or the will to co-operate with the crusaders, the Ottoman domination in Thrace would have ended even more suddenly than it had begun. But they made no move. In fact, one of the Byzantine historians charges John Palaeologos with aiding the Osmanlis![271] Lalashahin was able to draw from the garrisons of the recently occupied cities, and to send forward to meet the crusaders some ten thousand men under Hadji Ilbeki. It was the intention of Lalashahin to have this army act wholly on the defensive. If only Hadji Ilbeki could prevent their passing the Maritza, they would be turned southward towards Enos. By that time he felt sure that he could rely upon one of three things happening: dissensions would arise among the crusaders, the Greeks would be alarmed by the Serbian approach to Enos and the sea and attack the crusaders, or Murad would have time to bring his army across the Dardanelles. The one purpose of Lalashahin was to prevent the invasion of Thrace and the investment of Adrianople.