on the Slavic population became significant, with the purpose of trading slaves with the Ottoman Empire. The raids were catastrophic for both Muscovy and the Grand Duchy of Lithuania, and they largely prevented the settlement of the "Wild Fields" – the steppes extending from about south of Moscow to the Black Sea – and contributed to the development of the Cossacks. Impact on development Giovanni de Plano Carpini, the pope's envoy to the Mongol great khan, traveled through Kiev in February 1246 and wrote: The influence of the Mongol invasion on the territories of Kievan Rus' was uneven. Colin McEvedy (Atlas of World Population History, 1978) estimates the population of Kievan Rus' dropped from 7.5 million prior to the invasion to 7 million afterwards. Centres such as Kiev took centuries to rebuild and recover from the devastation of the initial attack. The Novgorod Republic continued to prosper, and new entities, the rival cities of Moscow and Tver, began to flourish under the Mongols. Moscow's eventual dominance of northern and eastern Rus' was in large part attributable to the Mongols. After the prince of Tver joined a rebellion against the Mongols in 1327, his rival prince Ivan I of Moscow joined the Mongols in crushing Tver and devastating its lands. By doing so he eliminated his rival, allowed the Russian Orthodox Church to move its headquarters to Moscow, and was granted the title of Grand Prince by the Mongols. As such, the Muscovite prince became the chief intermediary between the Mongol overlords and the Rus' lands, which paid further dividends for Moscow's rulers. While the Mongols often raided other areas of Rus', they tended to respect the lands controlled by their principal collaborator. This, in turn, attracted nobles and their servants who sought to settle in the relatively secure and peaceful Moscow lands. Although Rus' forces defeated the Golden Horde at the Battle of Kulikovo in 1380, Mongol domination of parts of Rus' territories, with the requisite demands of tribute, continued until the Great stand on the Ugra river in 1480. Historians argued that without the Mongol destruction of Kievan Rus', the Rus' would not have unified into the Tsardom of Russia and, subsequently, the Russian Empire would not have risen. Trade routes with the East went through Rus' territory, making them a center of trade between east and west. Mongol influence, while destructive to their enemies, had a significant long-term