Sigismond, beholding the crescent of the Moslem floating over the castles of eastern Hungary, became alarmed for the kingdom, and sent ambassadors from court to court to form a crusade against the invaders.  He was eminently successful, and an army of one hundred thousand men was soon collected, composed of the flower of the European nobility.  The republics of Venice and Genoa united to supply a fleet.  With this powerful armament Sigismond, in person, commenced his march to Constantinople, which city the Turks were besieging, to meet the fleet there.  The Turkish sultan himself gathered his troops and advanced to meet Sigismond.  The Christian troops were utterly routed, and nearly all put to the sword.  The emperor with difficulty escaped.  In the confusion of the awful scene of carnage he threw himself unperceived into a small boat, and paddling down the Danube, as its flood swept through an almost uninhabited wilderness, he reached the Black Sea, where he was so fortunate as to find a portion of the fleet, and thus, by a long circuit, he eventually reached his home.

Bajazet, the sultan, returned exultant from this great victory, and resumed the siege of Constantinople, which ere long fell into the hands of the Turks.  Amurath, who was sultan at the time of the death of Sigismond, thought the moment propitious for extending his conquests.  He immediately, with his legions, overran Servia, a principality nearly the size of the State of Virginia, and containing a million of inhabitants.  George, Prince of Servia, retreating before the merciless followers of the false prophet, threw himself with a strong garrison into the fortress of Semendria, and sent an imploring message to Albert for assistance.  Servia was separated from Hungary only by the Danube, and it was a matter of infinite moment to Albert that the Turk should not get possession of that province, from which he could make constant forays into Hungary.

Albert hastily collected an army and marched to the banks of the Danube just in time to witness the capture of Semendria and the massacre of its garrison.  All Hungary was now in terror.  The Turks in overwhelming numbers were firmly intrenched upon the banks of the Danube, and were preparing to cross the river and to supplant the cross with the crescent on all the plains of Hungary.  The Hungarian nobles, in crowds, flocked to the standard of Albert, who made herculean exertions to meet and roll back the threatened tide of invasion.  Exhausted by unremitting toil, he was taken sick and suddenly died, on a small island of the Danube, on the 17th of October, 1439, in the forty-third year of his age.  The death of such a prince, heroic and magnanimous, loving the arts of peace, and yet capable of wielding the energies of war, was an apparent calamity to Europe.