Slavs
Slavs can be further grouped by religion. Orthodox Christianity is practiced by the majority of Slavs. The Orthodox Slavs include the Belarusians, Bulgarians, Macedonians, Montenegrins, Russians, Serbs, and Ukrainians and are defined by Orthodox customs and Cyrillic script as well as their cultural connection to the Byzantine Empire (Serbs also use Latin script on equal terms). Their second most common religion is Roman Catholicism. The Catholic Slavs include Croats, Czechs, Kashubs, Moravians, Poles, Silesians, Slovaks, Slovenes, and Sorbs and are defined by their Latinate influence and heritage and connection to Western Europe. There are also substantial Protestant and Lutheran minorities especially amongst the West Slavs, such as the historical Bohemian (Czech) Hussites.
Ukrainian language
In the 19th century, the question of whether Ukrainian, Belarusian and Russian languages are dialects of a single language or three separate languages was actively discussed, with the debate affected by linguistic and political factors. The political situation (Ukraine and Belarus being mainly part of the Russian Empire at the time) and the historical existence of the medieval state of Kievan Rus', which occupied large parts of these three nations, led to the creation of the common classification known later as the East Slavic languages. The underlying theory of the grouping is their descent from a common ancestor. In modern times, Ukrainian, Russian, and Belarusian are usually listed by linguists as separate languages.