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The Principality or, from 1253, Kingdom of Galicia–Volhynia, also known as the Kingdom of Ruthenia or Kingdom of Rus/Russia, was a medieval state in Eastern Europe which existed from 1199 to 1349. Its territory was predominantly located in modern-day Ukraine, with parts in Belarus, Poland, Moldova, and Lithuania. Along with Novgorod and Vladimir-Suzdal, it was one of the three most important powers to emerge from the collapse of Kievan Rus'.

Roman the Great united the principalities of Galicia and Volhynia at the turn of the 13th century. Following the destruction wreaked by the Mongol invasion of Kievan Rus' (1239–1241), Prince Daniel of Galicia and the other princes of Rus' pledged allegiance to Batu Khan of the Golden Horde in 1246. The Polish conquest of the kingdom in 1349 led to it being fully absorbed by Catholic Poland. Upon annexing it in 1349, Polish king Casimir III the Great adopted the title of King of Poland and Ruthenia, and the territory was transformed into the Ruthenian Voivodeship (Latin: Palatinatus Russiae) in 1434.