Slavs
Slavs are the largest ethno-linguistic group in Europe. Present-day Slavic people are classified into East Slavs (chiefly Belarusians, Russians, Rusyns, and Ukrainians), West Slavs (chiefly Czechs, Kashubs, Moravians, Poles, Silesians, Slovaks and Sorbs), and South Slavs (chiefly Bosniaks, Bulgarians, Croats, Macedonians, Gorani, Pomaks, Montenegrins, Serbs and Slovenes).
Ukrainian language
Some scholars see a divergence between the language of Galicia-Volhynia and the language of Novgorod-Suzdal by the 12th century, assuming that before the 12th century, the two languages were practically indistinguishable. This point of view is, however, at variance with some historical data. In fact, several East Slavic tribes, such as Polans, Drevlyans, Severians, Dulebes (that later likely became Volhynians and Buzhans), White Croats, Tiverians and Ulichs lived on the territory of today's Ukraine long before the 12th century. Notably, some Ukrainian features were recognizable in the southern dialects of Old East Slavic as far back as the language can be documented.