The rise of Moscow during medieval times was a fundamental development in Russian history. Moscow began with very little and for a long time could not be compared to such flourishing principalities as Novgorod or Galicia. Even in its own area, the northeast, it was junior to old centers like Rostov and Suzdal. In accounting for Moscow's rise, historians have emphasized several factors or rather groups of factors. First, attention may be given to the doctrine of geographic causation. It stresses the decisive importance of the location on Moscow for the later expansion of the Muscovite state (the medieval state centered in Moscow) and includes several lines of argument. Moscow lay as a crossing of three roads. The most important was the way from the historically crucial city of Kiev and the declining south to the growing northeast. In fact Moscow has been described as the first stopping and setting point in the northeast. But it also profited from moments in other directions, including the reverse. Thus it seems immigrants came to Moscow after the Mongol devastation of the lands further to the northeast. Moscow was also situated on a bend of the Moscow River that flows from the northwest to the southeast into the Oka, the largest western tributary of the Volga River. To speak more broadly of water communications which span and unite European Russia, Moscow has the rare fortune of being located near the headwaters of four major rivers: the Oka, the Volga, the Don, and the Dnieper. This offered marvelous opportunities for expansion across the flowing plain, especially as there were no mountains or other natural obstacles to hem in the young principality. In another sense too, Moscow benefited from a central position. It stood in the midst of lands inhabited by the Russian people which, so the argument runs, provided a proper setting for a natural growth in all directions. In fact some specialists have tried to estimate precisely how close to the geographic center of the Russian people Moscow was situated, noting also such circumstances as proximity to the land dividing the two main dialects of the Great Russian language. Central location within Russia, to make an additional point, cushioned Moscow from outside invaders. Thus, for example, it was the city of Novgorod, not Moscow, that continuously had to meet enemies from the northwest, while in the southeast Riazan absorbed the first blows from the direction. All in all, the considerable significance of the location on Moscow cannot be denied although this geographic factor has generally been assigned less relative weight by recent scholars. The economic argument is linked in part to the geographic. The Moscow River served as an important trade artery, and as the Muscovite principality expanded around its waterways, it profited by and in turn helped to promote increasing economic intercourse. One school of thought has treated the expansion of Moscow largely in terms of the growth of a common market. Another economic approach emphasizes the success of the Muscovite princes in developing agriculture in their domains and supporting colonization. These princes clearly outdistance their rivals in obtaining peasants to settle on their lands. As a further advantage, they managed to maintain in their realm a relative peace and security highly beneficial to economic life. The last view introduces another key factor in explaining the Muscovite rise: the role of the rulers of Moscow. Moscow has generally been considered fortunate in its princes. Sheer luck constituted an important part of the picture. For several generations, the princes of Moscow had the advantage of male succession without interruption or conflict. In particular, for a long time the sons of the princes of Moscow were lucky not to have uncles competing for the Muscovite seat. When the classic power struggle between royal uncles and nephews finally erupted under Basil II (reigned 1425-1462), direct succession from father to son possessed sufficient standing and support in the principality of Moscow to overcome the challenge. The principality has also been considered fortunate because its early rulers, descending from the youngest son of Alexander Nevskii (1220?-1263) and thus representing a junior princely branch, found it expedient to devote themselves to their small holdings instead of neglecting them for more ambitious undertakings elsewhere.