LADISLAO II, Jagellone, king of POLAND. — Born in 1350, grand duke of Lithuania from 1377. The continual struggles against the Teutonic Knights and against his son Vitautas, who relied on them, induced him to accept the invitation of the Polish nobility that, by marrying Jadwiga d’Angiò, queen of Poland, he should unite his own destiny and that of his people with those of Poland. By the Act of Krewo of 1385, L. undertook to receive Baptism together with all his people and to bring about the fusion of the two States (what would later be called Unja Jagellońska). L. was baptized at Cracow in 1386, urged the Lithuanians to convert, and in 1387 was able to establish the first bishopric at Vilna.
Complete fusion of the two peoples was not achieved, however, since the Lithuanians continued to maintain their own individuality and L., in addition to being king of Poland, always remained dux supremus Lithuaniae. From that time the process began, on the Polish side, of the spontaneous assimilation of the Lithuanian nobility, which was admitted to sit in the Diet on an equal footing with the Polish zlachta. Thanks to the union of Krewo, Poland under L. Jagellone, besides continuing its victorious struggle against the Teutonic Knights, defeated in a decisive battle at Grünwald on 15 July 1410 (after which the Order was practically never again able to recover), gained the scope and role of a great power, since it adopted as its own those aims of expansion or simple influence toward the East, Kiev, and the Black Sea that had belonged to Great Lithuania. Thus the eastern horizons opened up for the Polish people as compensation and counterweight to the growing pressure and erosion exerted in the west by Germanism. Always opposed to the Hussite movement, L. died at Gródek (Leopoli) on 31 May 1434.