into slavery; while skilled laborers and artisans were sent to the Mongol's steppe regions. In the late 15th century, the Muscovite Grand Dukes began taking over former Kievan territories and proclaimed themselves the sole legal successors of the Kievan principality according to the protocols of the medieval theory of translatio imperii. Of the Rus' principalities, only Polatsk escaped the Mongol invasions of 1237–39, but Lithuania made it a vassal in 1240, annexed it in 1307, although it retained local autonomy into the 1390s. On the southwestern periphery, Kievan Rus' was succeeded by the Principality of Galicia-Volhynia. Later, as these territories, now part of modern central Ukraine and Belarus, fell to the Gediminids, the powerful, largely Ruthenized Grand Duchy of Lithuania drew heavily on Rus' cultural and legal traditions. From 1398 until the Union of Lublin in 1569 its full name was the Grand Duchy of Lithuania, Ruthenia and Samogitia. After the Union of Lublin, the southern parts of the Grand Duchy were joined to the remnants of Galicia-Volhynia, forming a split of Ruthenia in the Lesser Poland Province, Crown of the Kingdom of Poland. This would almost be the modern borders between northern and southern Ruthenia, or modern Ukraine and Belarus, which have historically been influenced by Poland and Lithuania respectively. On the north-eastern periphery of Kievan Rus', traditions were adapted in the Vladimir-Suzdal Principality that gradually gravitated towards Moscow. To the very north, the Novgorod and Pskov Feudal Republics were less autocratic than Vladimir-Suzdal-Moscow until they were absorbed by the Grand Duchy of Moscow. Modern historians from Belarus, Russia and Ukraine alike consider Kievan Rus' the first period of their modern countries' histories. Economy In the early 10th century, Kievan Rus' mainly traded with other tribes in Eastern Europe and Scandinavia. "There was little need for complex social structures to carry out these exchanges in the forests north of the steppes. So long as the entrepreneurs operated in small numbers and kept to the north, they did not catch the attention of observers or writers." The Rus' also had strong trading ties to Byzantium, particularly in the early 900s, as treaties in 911 and 944 indicate. These treaties deal with the treatment of runaway Byzantine slaves and limitations on the amounts of certain commodities such as silk that could be bought from Byzantium. The Rus' used log rafts floated down the Dnieper River by Slavic tribes for the transport