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.
Ukrainians
Differentiation between separate East Slavic groups began to emerge in the later medieval period, and an East Slavic dialect continuum developed within the Polish–Lithuanian Commonwealth, with the Ruthenian language emerging as a written standard. The active development of a concept of a Ukrainian nation and a Ukrainian language began with the Ukrainian National Revival in the early 19th century. In the Soviet era (1917–1991), official historiography emphasized "the cultural unity of 'proto-Ukrainians' and 'proto-Russians' in the fifth and sixth centuries".