LADISLAUS II JAGIELLO, King of POLAND. — Born in 1350, Grand Duke of Lithuania from 1377. Continuous struggles against the Teutonic Knights and against his son VYTAUTAS, who relied on them, led him to accept the invitation of the Polish nobility to unite his fate and that of his people with those of Poland by marrying JADWIGA of Anjou, Queen of Poland. Through the Union of Krewo in 1385, LADISLAUS assumed the commitment to receive Baptism together with his entire people and to effect the fusion of the two states (which would later be called the Union of Krewo). LADISLAUS was baptized in Cracow in 1386, urged the Lithuanians to convert, and in 1387 was able to found the first diocese in Vilnius.
However, complete fusion of the two peoples was not achieved, since the Lithuanians continued to maintain their own identity, and LADISLAUS, besides being King of Poland, always remained supremus dux Lithuaniae. From that time began the process of spontaneous assimilation of the Lithuanian nobility by the Poles, admitted to sit in the Diet on equal terms with the Polish szlachta. Thanks to the Union of Krewo, Poland under LADISLAUS JAGIELLO, besides continuing to fight victoriously against the Teutonic Knights—defeated in a decisive battle at Grunwald on 15 July 1410 (after which the Order was practically unable to recover)—acquired the breath and function of a great power, since it made its own those objectives of expansion or mere influence toward the East, Kiev, and the Black Sea which were proper to the Grand Duchy of Lithuania. Thus, new eastern horizons opened for the common people as compensation and counterbalance to the growing pressure and encroachment carried out in the West by Germanism. Always opposed to the Hussite movement, he died at Gródek (Leopoli) on 31 May 1434.