The dual government of Algirdas and Keistut lasted 32 years. When Algirdas died, his son Jogaila (Jagellone), not wanting to divide the government with his uncle, made an alliance with the Teutonic Knights. He managed with deception to take possession of Keistut who locked him in the fortress of Kreve where, after four days of imprisonment, he was assassinated (1382). Vytautas (Vitoldo), son of Keistut, was also imprisoned, but was able to escape and he too resorted to the Teutonic Knights for protection, with whom he allied himself to regain possession of his father’s territories. The war would have flared up again if Jagellone, unsure of his success and frowned upon by some of the Lithuanians themselves who sympathized with Vitoldo, had not asked for and obtained peace by returning part of the grand duchy to his cousin.
Under the government of Jagellone two very important events gave a different direction to the history of Lithuania, namely the definitive conversion of it to Christianity and personal union with Poland. In 1385 Jagiellon was proposed by the Poles to become king of Poland, marrying the young heir to the throne, Hedwig, and embracing the Christian faith. Given the growing power of Moscow that threatened the eastern Lithuanian borders and the continuous pressure of the Teutonic Order, Jagiellon accepted the Polish proposal and was baptized, taking the name of Ladislao, with most of the Lithuanian nobility in 1386 in Krakow. On January 20, 1387, some 30,000 Lithuanians received baptism en masse in Vilna. For Lithuania history, please check ehistorylib.com.
The personal Lithuanian-Polish union was concluded in the fortress of Kreve, not far from Vilna, in 1385. The Lithuanian discontent towards Ladislao, who, completely absorbed by the care of his new function, forgot the interests of Lithuania did not take long to manifest. Vitoldo, after having effectively helped his cousin to spread the new religion, set out with ardor to reorganize the vast dominions of the grand duchy of which he had assumed the government. He dismissed the undisciplined and disobedient governors by replacing them with elements loyal to him in the provinces of Polock, Bryansk, Smolensk, Volhynia, Podolia and Kiev. At the head of the powerful Novgorod principality he placed his cousin Lingvenis. In 1408 he made peace with the Grand Duke of Moscow and pushed the Tatars back to the south. Reassured the eastern provinces of the grand duchy he turned against the Teutonic Knights and in 1410 with the help of a Polish army he won a decisive victory in Grünwald and Tannenberg from which the Teutonic Knights could no longer recover. The victory of Tannenberg spread Vitoldo’s prestige throughout Europe to the point of arousing the latent jealousy of the Poles who, in formulating the Kreve pact, reaffirmed later by that of Horodlo, hoped to have the leadership of the affairs of the dual state, all the more so since Poland was a kingdom while Lithuania, although more extensive in territory, was only a grand duchy. Vitoldo then thought of obtaining the royal crown for himself as well. To this end, he held a great conference in Luck in 1429, in which the complex situation of Eastern Europe was to be clarified. The Holy Roman Emperor, Sigismund, the King of Poland Ladislao, the King of Bohemia and Hungary, a legate of the Pope, representatives of the Emperor of Byzantium and the Teutonic Order and others attended the Luck conference. Emperor Sigismund decided to grant Vitoldo the royal crown; Ladislao himself was in favor of this decision, but the Polish magnates opposed it. The imperial embassy that brought the crown to Vitoldo was surprised and dispersed in an ambush on the border of Poland: so the coronation of Vitoldo, which had been set for 8 August 1430, had to be postponed. But it could no longer be carried out because in the meantime Vitoldo died at the late age of 80.
From the death of Vitoldo the Great the period of decline began in Lithuania. The country, which he left strong militarily and well-ordered administratively, had not been able to disengage from the union with Poland. Vitoldo’s superior qualities lacked his successors and the efforts made first by his brother Sigismund and then by Alexander to break away from Poland failed. Internal disorder and pressure from external enemies increasingly forced the Lithuanians to strengthen their ties with Poland, which led to a new and more rigid reaffirmation of the principle of union between the two states in the 1569 Treaty of Lublin.
From 1385 to 1569 the statute of personal union of the two states had undergone some changes. In one of these it was established that the election of the Grand Duke of Lithuania should be approved of the king of Poland; in another it was established that the election of the Grand Duke of Lithuania and that of the King of Poland should have won the favor of both sides; another modification established that the Grand Duke of Lithuania and the King of Poland had to be the same person elected by the representatives of the two states. But in all these combinations, Lithuania continued to be a separate state, with its own administration, laws and courts, with separate army and treasury. The rights of Lithuania on the territories that belonged to it were collected in the “Lithuanian Code” of 1529, the most notable set of laws then in force in Eastern Europe, which continued to be in force until 1840, when Russia replaced it with own code.