The Varangians – the Vikings played the crucial role in the establishment of Kievan Rus. They built their trade centers in the eastern Baltic from where they penetrated deep into today’s Russia, Belarus and Ukraine, and traded with the Byzantine Empire and Asia. The primal goal of the Varangians was the quest for new markets and trade routes but it ended with occupation of today’s western Russia, Belarus and Ukraine where they established their kingdom – Kievan Rus.
Kievan Rus was established about 882 when prince Oleg, the ruler of Novgorod seized Kiev and made it his capital. His successors led successful campaigns against the Khazars, Pechenegs and Bulgarians, and several times endangered the Byzantine Empire. The Byzantines managed to repulse the Kievan aspirations through political means and achieved an alliance with Kievan Rus through marriage of Anna, sister of Byzantine Emperor Basil II and the Grand Prince of Kiev, Vladimir I (980-1015). Kievan Rus reached its zenith during the reign of Vladimir I and his successor Yaroslav I the Wise (1019-1054). The Golden Age of Kievan Rus also saw adoption of Christianity and increased influence of the Byzantine culture.
Kievan Rus began to decline in the second half of the 11th century mostly due to nomadic invasions and struggles over the throne. In the middle of the 12th century began to rise the regional centers of power: Halych on the west, Novgorod on the north, Vladimir-Suzdal on the northwest and Kiev on the south. However, Kievan forces were severely defeated by the Mongols in the Battle at Kalka River in 1223 and Kievan Rus was invaded and subjugated by the Mongols in 1237-1240.