Duchy of Belz [SEP] dissolved or abolished
of Masovia as a fiefdom of Poland and as a dowry for Siemowit's marriage with Jagiełło's sister, Alexandra. In 1462, after the death of Władysław II of Płock, the last of Siemowit's IV direct descendants, Casimir IV Jagiellon of Poland attempted to incorporate the entire Duchy of Masovia to Poland; eventually he succeeded only in incorporating the Duchy of Belz into the administrative structure of Poland as the Bełz Voivodeship (palatinate). Eventually, the Duchy of Masovia was incorporated in 1526. Belz remained part of Poland (
Duchy of Belz
Duchy of Belz or principality of Belz was a duchy, formed in the late 12th century in Kievan Rus. During its history the duchy was a constituent part of some other political entities such as the Kingdom of Rus, the Kingdom of Hungary, Duchy of Masovia when eventually in the late 14th century was incorporated into Poland becoming later the Bełz Voivodeship.
History.
The duchy formed in 1170 because of the feudal fragmentation of Kievan Rus' when the Volhynia region (centered at Volodymyr-Volynsky)