The duchy formed in 1170 because of the feudal fragmentation of
Kievan Rus'. The Volhynia region, centered on
Volodymyr, was passed to
Mstislav II of Kiev (died 1170), who later split it between his sons. Mstislav was married to
Agnes of Poland and in fierce opposition to
Yuri Dolgoruki. Being exiled to Poland for a short period of time, Mstislav was able to drive Dolgoruki out of
Volhynia. With time, the city of Belz and the surrounding territories were passed to
Vsevolod Mstislavich, who in turn passed it to his son Alexander. Alexander, a nephew of
Roman the Great, was deposed from Belz in 1234 by
Daniel of Galicia, who incorporated Belz into the
Duchy of Galicia–Volhynia (later the Kingdom of Rus), which would control Belz till 1340. 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 (later, the
Polish–Lithuanian Commonwealth) until its partitions in the late 18th century. ==Territory==