Galicia-Volhynia
A successor state to Kievan Rus' on part of the territory of today's Ukraine was the principality of Galicia-Volhynia. Previously, Vladimir the Great had established the cities of Halych and Ladomir (later Volodimer) as regional capitals for the western Ukrainian heartland. This new, more exclusively Ukrainian predecessor state was based upon the Dulebe, Tiverian and White Croat tribes. The state was ruled by the descendants of Yaroslav the Wise and Vladimir Monomakh. For a brief period, the country was ruled by a Hungarian nobleman. Battles with the neighboring states of Poland and Lithuania also occurred, as well as internecine warfare with the independent Ruthenian principality of Chernigov to the east. The nation reached its peak with the extension of rule to neighboring Wallachia/Bessarabia, all the way to the shores of the Black Sea.
During this period (around 1200–1400), each principality was independent of the other for a period of time. The state of Halych-Volynia eventually became a vassal to the Mongolian Empire, but efforts to gain European support for opposition to the Mongols continued. This period marked the first "King of Rus'"; previously, the rulers of Rus' were termed, "Grand Dukes" or "Princes."
Read more about this topic: History Of Ukraine