But there was to be still a period of fierce resistance to the Turk. In 1413 the Turks, dissatisfied with the attitude of the Serbs, entered upon a new invasion of the territory of Serbia. In 1440 Sultan Amurath II. again overran the country and conquered it definitely, imposing not merely vassalage but armed occupation on its people. John Hunyad, "the White Knight of Wallachia," came to the rescue of the Serbs, and Amurath II. was driven back. An alliance between Serbs and Hungarians kept the Turk at bay for a time, and in 1444 Serbia could claim to be free once again. But the respite was a brief one. In 1453 Constantinople fell to the Turks, and the full tide of their strengthened and now undivided power was turned upon Serbia. A siege of Belgrade in 1457 was repulsed, but in 1459 Serbia was conquered and annexed to European Turkey. Lack of unity among the Serbs themselves had contributed greatly to the national doom, but on the whole the Serbs had put up a gallant fight against the Turks. And even now a section of them, the Montenegrins, in their mountain fastnesses kept their liberty, and through all the centuries that were to follow never yielded to the Crescent. The condition of the Serbs in the fifteenth and sixteenth centuries was very unhappy. They could come to no manner of contentment with Turkish rule, and sporadic revolts were frequent. At times the Hungarians from the other side of the Danube came to the aid of the revolters, but never in such strength as to shake seriously the Turkish power. Very many of the Serbs left their country in despair and sought refuge under the Austrian flag. To-day a big Serb element, under the flag of Austro-Hungaria, is one of the racial difficulties of the Dual Monarchy. [Illustration: _Underwood & Underwood_ KING PETER OF SERBIA] The Serb exiles carried to their new homes their old sympathies, and largely because of their efforts Austria in 1788 went to the rescue of Serbia, and for a brief while the land again was free. But the Turkish power returned and Serbia stumbled blindly, painfully through years of reprisals, which culminated in the great massacre of Serbs by Turks in 1804, which, like the Turkish massacre of Bulgarians in 1875, really declared the doom of the Turkish power in the country. Following this massacre George Petrovic, "Black George," or "_Kara_ George," as the Serbians knew him, raised the standard of revolt among his countrymen. He was a fierce blood-stained man, this first liberator of the Serbs, a man on whose head was the blood of his father and his brother. His grim character was fitted for his grim task. The story of that task will come better within the scope of a following chapter, which will tell of the liberation of the Balkans from the Turks.