History, The Decline of Kievan Rus
After Yaroslav's death in 1054, Kievan Rus declined. The state's prosperity was highly dependent on its control of the major trade routes between northern Europe and the Byzantine Empire and the Middle East. In the 11th and 12th centuries the Turkic Polovtsy (Cuman) tribe conquered and dominated the southeastern steppe, threatening the Kievan Rus trade routes. Matters worsened after the Crusaders sacked Constantinople (present-day Istanbul) in 1204. The huge but sparsely populated lands between the Baltic and Black seas were difficult to hold together as a single state. Furthermore, because Kievan Rus territories were divided among a ruler's heirs, political power became fragmented and constant battles ensued between the various branches of the princely house.
Yaroslav's grandson, Vladimir II Monomakh, made the final attempt to unite Kievan Rus, but after his death in 1125 the fragmentation continued. Other Kievan Rus principalities challenged Kyiv's supremacy, particularly Galicia and Volhynia to the west; Chernigov, Novgorod-Severskiy, and Vladimir-Suzdal' to the northwest; Polotsk and Smolensk to the north; and Novgorod, by far the largest, in the far north.
Novgorod rose to a dominant position as a flourishing commercial state. In the 13th century the city became the site of a major factory of the Hanseatic League, a commercial confederation of European city-states. Kyiv also lost its importance as the great national and cultural center as Suzdal', Vladimir, and ultimately Moscow, surpassed it. The East Slavic lands became a loose federation of small principalities, held together by common language, religion, traditions, and customs. Although ruled by members of the house of Ryurik, these principalities were often at war with one another. Plundering along the frontiers also caused difficulties. In the west the Poles, Lithuanians, and Teutonic Knights encroached on East Slavic territory; the Polovtsy repeatedly raided the south. While all these posed significant threats to Kievan Rus, in the 13th century an even greater danger came from East Asia.