Casimir, King of Poland, who had long had hostile intentions against the order, secretly threw all his weight into the cause of the malcontents, who made such way that the grand master was forced to retire to Marienberg, his capital, where he was soon closely besieged.  Casimir now openly declared war, and laid claim to the dominions of the knights in Prussia and Pomerania, formally annexing them to the kingdom of Poland.

The grand master sent petitions for aid to the neighboring princes, but without success.  The kings of Denmark and Sweden excused themselves on account of the distance of their dominions from the seat of war.  Ladislaus, King of Bohemia and Hungary, was about to marry his sister to Casimir, and the religious dissensions of Bohemia and the attacks of the Turks upon Hungary fully occupied his attention and demanded the employment of all his troops and treasure; and finally the capture of Constantinople by Mahomet at this very time (1458) seemed to paralyze the energies of the European powers.

The grand master, Louis d’Erlichshausen, thus found himself deserted in his time of need.  He did what he could by raising a considerable body of mercenaries, and with these, his knights, and the regular troops of the order, he defended himself with courage and wonderful endurance, so that he not only succeeded in holding the city, but recovered several other towns that had revolted.

But his resources were unequal to the demands made upon them, his enemy overwhelmed him with numbers, his own soldiers clamored for their pay long overdue, and there was no prospect of aid from without.  There was nothing left, therefore, to him but to make the best terms he could.  He adopted the somewhat singular plan of making over Marienberg and what remained of the dominions of the order to the chiefs who had given him aid, in payment for their services, and he himself, with his knights and troops, retired to Koenigsberg, which then became the capital of the order.  Marienberg soon afterward came into the hands of Casimir; but the knights again captured it, and again lost it, 1460.

War continued year after year between Poland and the knights, the general result of which was that the latter were defeated and lost one town after another, till, in 1466, a peace was concluded, by the terms of which the knights ceded to Poland almost all the western part of their dominions, retaining only a part of Eastern Prussia, with Koenigsberg for their capital, the grand master acknowledging himself the vassal of the King of Poland, with the title of Prince and Councillor of the kingdom.

In 1497 the order lost its possessions in Sicily through the influence of the Pope and the King of Aragon, who combined to deprive it of them.  It still retained a house at Venice, and some other property in Lombardy.  In 1511 Albert de Brandenberg was elected grand master.  He made strenuous efforts to procure the independence of the order, and solicited the aid of the Emperor to free it from the authority of Poland, but without success.  The grand master refused the customary homage to the King of Poland, and, after fruitless negotiations, war was once more declared, which continued till 1521, when peace was concluded; one of the results of which was the separation of Livonia from the dominion of the order, and its erection into an independent state.