The history of Russian language may be divided into the following periods.
Kievan period and feudal breakup
The Tatar yoke and the Grand Duchy of Lithuania
The Moscovite period (15th–17th centuries)
Empire (18th–19th centuries)
Soviet period and beyond (20th century)
Judging by the historical records, by approximately 1000 AD the predominant ethnic group over much of modern European Russia, Ukraine, and Belarus was the Eastern branch of the Slavs, speaking a closely related group of dialects. The political unification of this region into Kievan Rus'in about 880, from which modern Russia, Ukraine and Belarus trace their origins, established Old East Slavic as a literary & commercial language. It was soon followed by the adoption of Christianity in 988 and the introduction of the South Slavic Old Church Slavonic as the liturgical and official language. Borrowings and calques from Byzantine Greek began to enter the Old East Slavic and spoken dialects at this time, which in their turn modified the Old Church Slavonic as well.
Dialectal differentiation accelerated after the breakup of Kievan Rus in approximately 1100. On the territories of modern Belarus and Ukraine emerged Ruthenian and in modern Russia; medival Russian. They definitely became distinct in 13th century by the time of division of that land between the Grand Duchy of Lithuania on the west and independent Novgorod Feudal Republic plus small duchies which were vassals of the Tatars on the east.Free Quote
The official language in Moscow and Novgorod, and later, in the growing Moscow Rus', was Church Slavonic which evolved from Old Church Slavonic and remained the literary language until the Petrine age, when its usage shrank drastically to biblical and liturgical texts.Russian with a strong influence of the Church Slavonic until the close of the seventeenth century, but, despite attempts at standardization, as by Meletius Smotrytsky c. 1620, its purity was by then strongly compromised by an incipient secular literature. The political reforms of Peter the Great were accompanied by a reform of the alphabet, and achieved their goal of secularization and Westernization. Blocks of specialized vocabulary were adopted from the languages of Western Europe. By 1800, a significant portion of the gentry spoke French, less often German, on an everyday basis. Many Russian novels of the 19th century, e.g. Lev Tolstoy's "War and Peace", contain entire paragraphs and even pages in French with no translation given, with an assumption that educated readers won't need one.
The modern literary language is usually considered to date from the time of Aleksandr Pushkin in the first third of the nineteenth century. Pushkin revolutionized Russian literature by rejecting archaic grammar and vocabulary (so called "высокий штиль" — "high style") in favor of grammar and vocabulary found in the spoken language of the time. Even modern readers of younger age may only experience slight difficulties understanding some words in Pushkin's texts, since only few words used by Pushkin became archaic or changed meaning. On the other hand, many expressions used by Russian writers of the early 19th century, in particular Pushkin, Lermontov, Gogol, Griboedov, became proverbs or sayings which can be frequently found even in the modern Russian colloquial speech. Since Russian classical literature is considered by most Ukrainians and Belarusians as the Common Russian or Common East-Slavonic literature, this phenomenon also applies to Ukrainian and Belarusian speakers.
The political upheavals of the early twentieth century and the wholesale changes of political ideology gave written Russian its modern appearance after the spelling reform of 1918. Political circumstances and Soviet accomplishments in military, scientific, and technological matters (especially cosmonautics), gave Russian a world-wide prestige, especially during the middle third of the twentieth century.