Sclaveni in the context of "Old Church Slavonic"

Old Church Slavonic (OCS) or Old Slavonic (/sləˈvɒnɪk, slæˈvɒn-/ slə-VON-ik, slav-ON-) is the first Slavic literary language and the oldest extant written Slavonic language attested in literary sources. It belongs to the South Slavic subgroup of the Balto-Slavic branch of the Indo-European language family and remains the liturgical language of many Christian Orthodox churches.

Historians credit the 9th-century Byzantine missionaries Saints Cyril and Methodius with standardizing the language and undertaking the task of translating the Gospels and necessary liturgical books into it as part of the Christianization of the Slavs. It is thought to have been based primarily on the dialect of the 9th-century Byzantine Slavs living in the Province of Thessalonica (in present-day Greece).

The siege of Constantinople in 626 by the Sassanid Persians and Avars, aided by large numbers of allied Slavs, ended in a strategic victory for the Byzantines. The failure of the siege saved the empire from collapse, and, combined with other victories achieved by Emperor Heraclius (r. 610–641) the previous year and in 627, enabled Byzantium to regain its territories and end the destructive Roman–Persian Wars by enforcing a treaty with borders status quo c. 590.

The culture of Croatia has historically been influenced by Central European, Mediterranean, and Balkan cultures. Croatia's unique culture and identity can be traced back to the historical llyricum. The early Croatian cultural and political identity developed through the integration of the ancient Roman heritage of Dalmatia, the traditions of early Slavic groups who settled in the region during the Migration period, and the emergence of a distinct Croatian polity by the 9th century. The Croatian language is believed to have been formed in the 6th or 7th century, with the written language present in Glagolitic texts from the 11th century.

In terms of Croatian national emancipation, the 19th-century Illyrian movement led by Ljudevit Gaj was a key driver for emergence of Croatian romantic nationalism. In 1842, the Matica ilirska organization (renamed Matica hrvatska in 1872) was established as part of the Zagreb Reading Room. The organization's mission was to promote Croatian national and cultural identity in fields of arts, science spiritual creation, economy, and public life. In 1847-1848 Croatian language replaced Latin as official language in Croatia.

The history of Bosnia and Herzegovina in the Middle Ages refers to the time period between the Roman era and the 15th-century Ottoman conquest. The Early Middle Ages in the Western Balkans saw the region reconquered from barbarians (Ostrogoths) by the Byzantine Emperor Justinian I (r. 527–565), followed by raids and migrations carried out by Slavic peoples in the 6th and 7th centuries. The first mention of a distinct Bosnian region comes from the 10th-century Byzantine text De Administrando Imperio. By the late 9th and early 10th century, Latin priests had Christianized much of Bosnia, with some areas remaining unconverted. In the High Middle Ages, Bosnia experienced economic stability and peace under the Ban Kulin who ruled over Banate of Bosnia from 1180 to 1204 and strengthened its ties with the Republic of Ragusa and with Venice. The Kingdom of Bosnia emerged in the Late Middle Ages (1377). The kingdom faced internal and external conflicts, eventually falling under Ottoman rule in the late 15th and early 16th centuries.

The White Croats (Croatian: Bijeli Hrvati; Polish: Biali Chorwaci; Slovak: Bieli Chorváti; Ukrainian: Білі хорвати, romanized: Bili khorvaty), also known simply as Croats, were a group of Early Slavic tribes that lived between East Slavic and West Slavic tribes in the historical region of Galicia north of the Carpathian Mountains (in modern Western Ukraine and Southeastern-Southern Poland), and in Northeastern Bohemia.

Debates continue over the origin of the Croats and related topics. Their ethnonym is usually considered to be of Iranian origin, and historians regard them one of the oldest Slavic tribes or tribal alliances that formed prior to the 6th century CE. They were an East Slavic tribe, but bordered both East Slavic groups (Dulebes and their related Buzhans and Volhynians, Tivertsi, and Ulichs) in Western Ukraine; and West Slavic tribes (Lendians and Vistulans) in southeastern Poland, controlling an important trade route from East to Central Europe. Archaeologically the Croats were mostly related to the Korchak and Luka-Raikovetska cultures identified with the Sclaveni (while their connection to the Antes and to the Penkovka culture remains a matter of dispute). Their area is characterized by use of stone defenses, tiled tombs (and kurgan-like tombs), stone ovens, and many large, fortified settlements and cult buildings. They practiced Slavic paganism. Foreign medieval authors documented the Croats in historical sources and legends, and had their own origo gentis.

The Byzantine–Serbian wars were a series of wars between the Byzantine Empire and the medieval Serbian states. Starting with the Sclaveni and Antae migrations into the Balkans, the succession of medieval Serbian states went through several periods of warfare with the Eastern Roman Empire.