The history of Belarus begins with the migration and expansion of the Slavs throughout Eastern Europe between the 6th and 8th centuries of the Common Era. East Slavs settled on the territory within present-day Belarus, Russia and Ukraine, assimilating local Baltic (Belarus), Ugro-Finnic (Russia) and steppe nomads (Ukraine) already living there, early ethnic integrations that contributed to the gradual differentation of the three East Slavic nations. These East Slavs were pagan, animistic, agrarian people whose economy included trade in agricultural produce, game, furs, honey, beeswax and amber.
During the 9th and 10th centuries, the Rus tribe of the Scandinavian Vikings established trade posts on the way from Scandinavia to Byzantine Empire. The network of lakes and rivers crossing East Slav territory provided a lucrative trade route between the two civilizations. In the course of trade, they gradually took sovereignty over tribes of East Slavs, at least to the point required by improvements in trade. The Rus rulers on few occasions invaded the Byzantine Empire, but eventually they became their ally against the Bulgars. The condition underlying this alliance was to open the country for Christianization and acculturation from the Byzantine Empire. The common cultural bond of Eastern Orthodox Christianity and written Church Slavonic (a literary and liturgical Slavic language developed by 8th-century missionaries Cyril and Methodius) fostered the emergence of a new geopolitical entity, Rus' -- a loose-knit network of principalities, established along preexisting trade routes, with major centers in Novgorod (Russia), Polatsk (Belarus) and Kyiv (Ukraine) — which claimed a sometimes precarious preeminence among them.
Between the 9th and 12th centuries, the principality of Polatsk (northern Belarus) emerged as the dominant center of power on Belarusian territory, with a lesser role played by the principality of Turaw in the south. It repeatedly asserted its sovereignty in relation to other centers of Rus', becoming a political capital, the episcopal see of a bishopric and the controller of vassal territories among Balts in the west. The city's Cathedral of the Holy Wisdom (1044-1066) remains a symbol of this independent-mindedness, rivaling churches of the same name in Novgorod and Kyiv, referring to the original Hagia Sophia in Constantinople (and hence to claims of imperial prestige, authority and sovereignty). Cultural achievements of the Polatsk period include the work of the nun Euphrosyne of Polatsk (1120-1173), who built monasteries, transcribed books, promoted literacy and sponsored art (including local artisan Lazarus Bohsha's famous "Cross of Euphrosyne," a national symbol and treasure stolen during World War II), and the prolific, original Church Slavonic sermons and writings of Bishop Cyril of Turaw (1130-1182).
In the 13th century, the fragile unity of Rus' disintegrated due to nomadic incursions from Asia, which climaxed with the Mongol Horde's sacking of Kyiv (1240), leaving a geopolitical vacuum in the region. The East Slavs splintered along preexisting tribal lines into a number of independent and competing principalities. Due to military alliances, dynastic marriages and previous assimilation, the Belarusian principalities gravitated toward the expanding Lithuanians, beginning with the rule of Prince Mindowh (1240-1263). From the 13th to 15th centuries, Baltic, Belarusian and Ukrainian lands were consolidated into the multi-ethnic Grand Duchy of Lithuania, Rus' and Samogitia, with its capital in Navahradak (in western Belarus) and later in Vilnius (in the Belarusian-Lithuanian borderland). The Lithuanians' smaller numbers and lack of written language or Christian culture in this medieval state gave the Belarusians and Ukrainians a major and important role in shaping Lithuanian political, religious and cultural life, and further assimilation between the Slavs and Balts occurred. Owing to the predominance of East Slavs among the state's population and ties with greater Europe that literacy, Christianity and culture facilitated, Old Belarusian became the official language of the Grand Duchy of Lithuania, Rus' and Samogitia, used for its official chancery, legal, diplomatic and judicial needs until 1696, when it was eventually replaced by Polish.
This period of political breakdown and reorganization also saw the rise of written local vernaculars in place of the literary and liturgical Church Slavonic language, a further stage in the evolving differentation between the Belarusian, Russian and Ukrainian languages.
After 1385 see also History of Poland, Polish-Lithuanian Commonwealth.
