In fifteen months the Osmanlis had become masters of the principal strategic points in Thrace. This great campaign, undertaken and carried through under the spur of necessity, was an auspicious beginning for the reign of Murad and for the supremacy of the Osmanlis in the Balkan peninsula. Europe was suffering from another visitation of the Black Death.[257] The Balkan nations were completely demoralized. So unpopular was John Palaeologos in his own capital that Murad contemplated entering into a conspiracy with some Byzantine traitors to have John assassinated and complete the conquest of the empire.[258] If he did enter fully into this plot, it was as fortunate for him that the undertaking failed as it was for the Bulgarians in 1912 that their columns did not pierce the lines of Ottoman defence at Tchataldja. For the disaster that follows a too extended and too rapid subjugation of unassimilated masses is as sudden as it is irreparable. Durable empire-building is governed by a law of homogeneity. The Osmanlis were still a race of limited numbers, and at the beginning of their existence as a nation. The process of assimilating the racial elements in conquered territories, begun by Osman when he first left the village of Sugut, could not be arrested; for the existence of the Ottoman state depended upon its continuance. The Greek of Bithynia had lived with Turk and Moslem for two centuries, and had found him a good neighbour. There was neither racial antipathy nor abhorrence of the religion of Mohammed to overcome. Nor had there been the hatred and dread of the conquered on the one side and the arrogance of the conqueror on the other. The Anatolian Greeks had been accustomed for generations to the economic and political conditions that finally caused the majority of them to cast their fortunes with the rising star of the Osmanlis. The problem of assimilating the Christians, who formed the total population of the Balkan peninsula, was a new one. Here were huge and compact masses of Christians, who had come suddenly under the yoke of the Osmanlis in the first two years of Murad’s reign. They did not know their new masters. They did not know Islam. Benevolent assimilation by voluntary conversion seemed no longer possible. A radical change in the attitude of the Osmanlis towards the question of religion was demanded. Wholesale massacre was impracticable, for the Osmanlis had no reserve of colonists to call upon to replace the indigenous elements. Their position was still too precarious to allow them to draw freely from their adherents in the corner of Asia Minor under their dominion. To win the Macedonians and Thracians by forcible conversion was not feasible. It required the expenditure of all his military resources for Murad to hold what he had conquered. He could not add police duty to his already superhuman burden. Even had he thought of this method of conversion, he would have been deterred by the nightmare of a crusade.