It is convenient to halt here and to retrace the steps of the Ottoman conquerors from the accession of Manuel, in 1391, with more care than was necessary in describing their direct attacks upon the empire. The number of Turks in Asia Minor and in Europe had now so much increased that their leaders began to dream, perhaps were already planning, the conquest of as wide a territory as had fallen before the immediate successors of the prophet. They had already almost succeeded in completing a ring of conquered states round Constantinople itself. The defeat of the Bulgarians and South Serbians on the Maritza, the great victory over the Serbians at Cossovo-pol, in 1389, enabled them to join forces with the Turks in the Morea and at isolated places on the eastern shore of the Adriatic. Nearly all Asia Minor acknowledged the rule of the Ottomans, and it was to the European portion of the empire that the attention of the Turk would now be turned.[112] An observer looking back upon all that was going on in Eastern Europe during the first half of the fifteenth century can now see that all the great events were part of a gigantic struggle against the hordes of Asia, represented by the Turks on the south of the Danube and in Asia Minor and the races whom it is convenient to call Tartars to the north of that river. The humiliation of the emperors to obtain aid from the West, the proceedings at Florence, the repeated calls upon Hungary and other Christian nations, were all incidents of that struggle. The statesmen of the West were gradually learning that the Ottomans had developed into a nation of fighters, and that it was not merely the remnant of the Greek empire which was threatened, but Christendom itself. [Sidenote: Reign of Sultan Bajazed, 1389–1403.] Upon the assassination of Murad at Cossovo-pol, his son Bajazed became sultan. He had already acquired, or acquired shortly after his accession, the nickname of _Ilderim_ or the Thunderbolt. He commenced his reign by strangling his elder brother, Jacoub. Ducas declares that he was an irreconcilable enemy of the Christian name and a passionate follower of Mahomet. During the reign of his predecessor, the struggle between the empire and the Turks had taken a theological character, and it is beyond reasonable doubt that religious animosity of a kind which had not shown itself among the first armies of the Turks had now diffused its baneful influence among the Ottoman armies. Under Bajazed, this fanaticism was intensified to such an extent that it led to cruelties of which it may be said that it is hardly possible to believe that even Mongol barbarity was ever greater than that exercised by the followers of the successor of Murad against Christians.