Russophones in Ukraine

The Russian language is the most common first language in the Donbass and Crimea regions of Ukraine, and the predominant language in large cities in the East and South of the country. The usage and status of the language (currently Ukrainian is the only state language of Ukraine) is an object of political disputes within Ukrainian society. Nevertheless, Russian is a widely used language in Ukraine in pop culture and informal and business communications.

The East Slavic languages originated in the language spoken in Rus. Significant differences in spoken language in different regions began to be noticed after the division of the Rus lands between the Golden Horde (from about 1240) and the Grand Duchy of Lithuania. Lithuania eventually allied with the Kingdom of Poland in the Polish–Lithuanian Commonwealth. Muscovites under the Golden Horde developed the modern Russian language, people in the northern Lithuanian sector developed Belorussian, and in the southern Polish sector Ukrainian.

It is worth noting that the ethnonym Ukrainian for the people was not well established until the 19th century, although their land was known as Ukraine in English since before the 18th century. The land was known in the West as Ruthenia, and the people as Ruthenians. (The Oxford English Dictionary traces the word "Ukrainian" in English back as far as 1804.) The Russian imperial centre, however, preferred the names "Little" and "White" Russias for the Ukrainian and Belarusian lands respectively, as compared to Great Russia.

No definitive geographical border separated people speaking Russian and those speaking Ukrainian - rather gradual shifts in vocabulary and pronunciation marked the areas between the historical cores of the languages. Since the 20th century, however, people have started to identify themselves with their spoken vernacular and to conform to the literary norms set by academics.

...
Wikipedia