Pannonian Avars in the context of "Volga Bulgaria"

Sofia is the capital and largest city of Bulgaria. It is situated in the Sofia Valley at the foot of the Vitosha mountain, in the western part of the country. The city is built west of the Iskar river and has many mineral springs, such as the Sofia Central Mineral Baths. It has a humid continental climate.

Known as Serdica in antiquity, Sofia has been an area of human habitation since at least 7000 BC. The recorded history of the city begins with the attestation of the conquest of Serdica by the Roman Republic in 29 BC from the Celtic tribe Serdi. During the decline of the Roman Empire, the city was raided by Huns, Visigoths, Avars, and Slavs. In 809, Serdica was incorporated into the First Bulgarian Empire by Khan Krum and became known as Sredets. In 1018, the Byzantines ended Bulgarian rule until 1194, when it was reincorporated by the Second Bulgarian Empire. Sredets became a major administrative, economic, cultural and literary hub until its conquest by the Ottomans in 1382. From 1530 to 1836, Sofia was the regional capital of Rumelia Eyalet, the Ottoman Empire's largest and most important province. Bulgarian rule was restored in 1878. Sofia was selected as the capital of the Third Bulgarian State in the next year, ushering a period of intense demographic and economic growth.

Old Great Bulgaria (Medieval Greek: Παλαιά Μεγάλη Βουλγαρία, Palaiá Megálē Voulgaría), also often known by the Latin names Magna Bulgaria and Patria Onoguria ("Onogur land"), was a 7th-century Turkic nomadic empire formed by the Onogur-Bulgars on the western Pontic–Caspian steppe (modern southern Ukraine and southwest Russia). Great Bulgaria was originally centered between the Dniester and lower Volga.

The original capital was Phanagoria on the Taman Peninsula between the Black and Azov seas. In the mid-7th century, Great Bulgaria expanded west to include Avar territory and was centered on Poltava. During the late 7th century, however, an Avar-Slavic alliance in the west, and Khazars in the east, defeated the Bulgars, and Great Bulgaria disintegrated. Successor states are the First Bulgarian Empire and Volga Bulgaria.

The Migration Period (c. 300 to 600 AD), also known as the Barbarian Invasions, was a period in European history marked by large-scale migrations that saw the fall of the Western Roman Empire and subsequent settlement of its former territories by various tribes, and the establishment of post-Roman kingdoms there.

The term refers to the important role played by the migration, invasion, and settlement of various tribes, notably the Burgundians, Vandals, Goths, Alemanni, Alans, Huns, early Slavs, Pannonian Avars, Bulgars and Magyars within or into the territories of Europe as a whole and of the Western Roman Empire in particular. Historiography traditionally takes the period as beginning in AD 375 (possibly as early as 300) and ending in 568. Various factors contributed to this phenomenon of migration and invasion, and their role and significance are still widely discussed.

Hungary is a landlocked country in Central Europe. Spanning much of the Carpathian Basin, it is bordered by Slovakia to the north, Ukraine to the northeast, Romania to the east and southeast, Serbia to the south, Croatia and Slovenia to the southwest, and Austria to the west. Hungary lies within the drainage basin of the Danube River and is dominated by great lowland plains. It has a population of 9.6 million, consisting mostly of ethnic Hungarians (Magyars) and a significant Romani minority. Hungarian is the official language, and among the few in Europe outside the Indo-European family. Budapest is the country's capital and largest city, and the dominant cultural and economic centre.

Prior to the foundation of the Hungarian state, various peoples settled in the territory of present-day Hungary, including the Celts, Romans, Huns, Germanic peoples, Avars and Slavs. Hungarian statehood is traced to the Principality of Hungary, which was established in the late ninth century by Álmos and his son Árpád through the conquest of the Carpathian Basin. King Stephen I ascended the throne in 1000 and converted his realm to a Christian kingdom. The medieval Kingdom of Hungary was a European power, reaching its height in the Late Middle Ages.

Slovakia, officially the Slovak Republic, is a landlocked country in Central Europe. It is bordered by Poland to the north, Ukraine to the east, Hungary to the south, Austria to the west, and the Czech Republic to the northwest. Slovakia's mostly mountainous territory spans about 49,000 km (19,000 sq mi), hosting a population exceeding 5.4 million. The capital and largest city is Bratislava, while the second largest city is Košice.

The Slavs arrived in the territory of the present-day Slovakia in the 5th and 6th centuries. From the late 6th century, parts of modern Slovakia were incorporated into the Avar Khaghanate. In the 7th century, the Slavs played a significant role in the creation of Samo's Empire. When the Avar Khaghanate dissolved in the 9th century, the Slavs established the Principality of Nitra before it was annexed by the Principality of Moravia, which later became Great Moravia. When Great Moravia fell in the 10th century, the territory was integrated into the Principality of Hungary at the end of the 9th century, which later became the Kingdom of Hungary in 1000. In 1241 and 1242, after the Mongol invasion of Europe, much of the territory was destroyed, but was recovered largely thanks to Hungarian king Béla IV. During the 16th and 17th centuries, southern portions of present-day Slovakia were incorporated into provinces of the Ottoman Empire. The Ottoman-controlled areas were ceded to the Habsburgs by the turn of the 18th century. The Hungarian declaration of independence in 1848 was followed in the same year by the Slovak Uprising through the establishment of the Slovak National Council. While the uprising did not achieve its aim, it played an important role in cementing a Slovak national identity. The Hungarian wars of independence eventually resulted in a compromise that established the Austro-Hungarian Empire.

The Duchy of Croatia (Modern Croatian: Kneževina Hrvatska; also Duchy of the Croats, Modern Croatian: Kneževina Hrvata; Latin: Ducatus Chroatorum; Greek: Χρωβατία) was a medieval state that was established by White Croats who migrated into the area of the former Roman province of Dalmatia c. 7th century AD. Throughout its existence the Duchy had several seats – namely, Klis, Solin, Knin, Bijaći and Nin. It comprised the littoral – the coastal part of today's Croatia – except Istria, and included a large part of the mountainous hinterland as well.

The Croats settled in Dalmatia after defeating the Pannonian Avars, during the time of Byzantine emperor Heraclius I. The Duchy was in the center of competition between the Byzantine Empire and the Carolingian Empire for rule over the area. Croatian rivalry with Venice emerged in the first decades of the 9th century and would continue through the following centuries. Croatia also waged battles with the Bulgarian Empire (founded c. 681; Bulgar-Croatian relations improved greatly afterwards) and with the Arabs; it also sought to extend its control over important coastal city-states under the rule of Byzantium. Croatia experienced periods of vassalage to the Franks or to the Byzantines and of de facto independence until 879, when Duke Branimir was recognized as an independent ruler by Pope John VIII. The Duchy was ruled by the Trpimirović and Domagojević dynasties from 845 to 1091. Around 925, during the rule of Tomislav, Croatia became a kingdom.

Great Moravia (Latin: Regnum Marahensium; Greek: Μεγάλη Μοραβία, Meghálī Moravía; Czech: Velká Morava [ˈvɛlkaː ˈmorava]; Slovak: Veľká Morava [ˈvɛʎkaː ˈmɔrava]; Polish: Wielkie Morawy, German: Großmähren), or simply Moravia, was the first major state that was predominantly West Slavic to emerge in the area of Central Europe, possibly including territories which are today part of the Czech Republic, Slovakia, Hungary, Austria, Germany, Poland, Romania, Croatia, Serbia, Ukraine and Slovenia. The formations preceding it in these territories were Samo's tribal union (631–658) and the Pannonian Avar state (567–822).

Centered on the Morava River – which gave the realm its name – the core encompassed today’s Moravia in the eastern Czech Republic and adjacent western Slovakia. The kingdom saw the rise of the first-ever Slavic literary culture in the Old Church Slavonic language as well as the expansion of Christianity, first via missionaries from East Francia, and later after the arrival of Saints Cyril and Methodius in 863 and the creation of the Glagolitic alphabet, the first alphabet dedicated to a Slavic language. Glagolitic was subsequently replaced by the Cyrillic alphabet created in the First Bulgarian Empire.