Pact of Vilnius and Radom
The Pact of Vilnius and Radom was a set of three acts passed in Vilnius, Grand Duchy of Lithuania, and confirmed by the Crown Council in Radom, Kingdom of Poland in 1401. The union amended the earlier act of the Union of Krewo and confirmed the Ostrów Agreement. Vytautas was granted the title of Grand Duke of Lithuania alongside Władysław II Jagiełło, King of Poland, who reserved his rights of an overlord, effectively making them formal coregents, with Jagiełło a dominant one as "Supreme Duke". After the death of Vytautas, Lithuania was to be ruled by Władysław II Jagiełło or his legal heir. The union is generally seen as strengthening of the Polish–Lithuanian union.
Background
Both Władysław II Jagiełło, King of Poland, and his cousin Vytautas, who ruled Lithuania on his behalf, sought to renew the Polish–Lithuanian union, which had existed since 1385. In 1399, King Jadwiga of Poland died due to childbirth complications, leaving Władysław II Jagiełło king of a foreign land and without an heir. If Polish nobles forced Władysław II Jagiełło to abdicate the throne, he would return to Lithuania demanding the throne of the Grand Duke. Vytautas would be forced either to return to Duchy of Trakai or launch another civil war. The same year Vytautas suffered a major defeat in the Battle of the Vorskla River against the Golden Horde and faced rebellions in the Principality of Smolensk, Republic of Pskov, and Velikiy Novgorod.Provisions
Negotiations began in late December 1400 in Hrodna. The union was signed in three separate acts: one by Władysław II Jagiełło, another by Vytautas and the Lithuanian nobles, and the third by the Polish Royal Council. It is significant that for the first time the Lithuanian nobles issued a political act in their own name, not merely as witnesses to the Grand Duke's treaties.Vytautas was instituted as the Grand Duke of Lithuania while his cousin Władysław II Jagiełło, King of Poland, retained the rights of an overlord. The union legalized Vytautas status as an actual ruler of Lithuania and his right to use title of "grand duke" alongside Władysław. However, this independence was to be temporary – after Vytautas' death Lithuania was to be governed by Władysław II Jagiełło or his legal heir and will become part of the kingdom and crown of Poland. The Polish and Lithuanian nobles agreed not to elect a new King of Poland without consulting each other. At the time neither Władysław II Jagiełło nor Vytautas had heirs, but each hoped to sire legitimate sons that would inherit both the Kingdom of Poland and the Grand Duchy. Vytautas also renewed his vows to Jagiełło, to the crown, kingdom, and inhabitants of Poland and promised to aid them when necessary.