structural:scholar_edition, stylistic:tone
Origins

The Principality of Volhynia may have emerged as early as the late 10th century, with Vsevolod, a son of Vladimir I of Kiev, mentioned as a prince of the city of Volodymyr. Igor Yaroslavich reportedly briefly reigned as the prince of Volodymyr in the 1050s. Iaroslav Sviatopolkovich (r. 1100–1118) was the only prince in Kievan Rus' to oppose Vladimir II Monomakh 's reign on the grounds of agnatic seniority, but after Vladimir ousted him in 1118, his Monomakhovichi descendants established a local dynastic branch. Roman Mstislavich, the great-great-grandson of Monomakh, inherited the throne of Volhynia in 1170.

The Principality of Galicia was formed in the years 1124–1144 by Vladimirko Volodarovich 's unification of the principalities of Zvenyhorod, Peremyshl, and Terebovlia. Since the 1080s or 1090s, all three had been ruled by sons of prince Rostislav of Tmutarakan, who may or may not also have been a prince in Volhynia and Galicia c. 1054/1060 to 1067.

Both Volhynia and Galicia had experienced a remarkable economic development in the 12th century due to their commercial advantages. In part, this was because land trade routes in Asia Minor were severely disrupted due to the Byzantine–Seljuk wars (1046–1243), diverting numerous merchants coming from the east heading for Constantinople via Alexandria in Egypt, while others circumvented Anatolia via the port of Sudak (Sougdaia) in Crimea. The flourishing of the latter commercial hub soon attracted Kievan Rus' traders, who rerouted some of the would-be Byzantine goods (occasionally through itinerant Jewish merchants) to Poland, Hungary, Bohemia and Germany, via the towns of Volhynia and Galicia.

Their new status as transit hubs for commerce between the northern Black Sea ports and central Europe brought Galicia and Volodimer-in-Volhynia tremendous wealth and increasing political power in the late 12th century. Trade and salt mining in particular empowered the boyar class of Galicia, who were able to challenge and undermine the authority of the Rostislavichi princes. Galicia and Volhynia merged around 1198 or 1199 into the principality of Galicia–Volhynia. This happened when the local Galician branch of the Rostislavichi clan died out, and Roman Mstislavich of Volhynia also took possession of Galicia, establishing a dynastic union.