By the beginning of the 9th century, after Avar Wars, that state was destroyed and replaced by the supreme rule of the Frankish Empire, which lasted until the Magyar conquest (c.

[5] During the reign of Byzantine Emperor Justin II (565–578), and following the Lombard-Gepid War in 567, Pannonia was invaded by Avars who subsequently conquered almost entire Pannonian Plain (568).

[18] He was joined by the Carantanians, Carniolans, reportedly Slavs around Salzburg and was supported by Fortunatus II [de] (Patriarch of Grado) - which was a substantial threat as their strength partly mirrored the former Avar Khaganate.

[20][21] However, the exact boundaries of his principality are uncertain as the term of Lower Pannonian could have implied both the lands between the river Drava and Sava as well as north of them and east of them in the former Roman province Pannonia Secunda (today's Syrmia).

[17] Possibly his rule expanded further to the east because in the historical sources is said to have been joined by the tribe of Timočani who lived around Timok Valley (in today's eastern Serbia).

[18] After Ljudevit's failed uprising and death,[22] in 827 the Bulgars under Great Khan Omurtag invaded and conquered Lower Pannonia and parts of Frankish territories to the north.

One of them probably was early Duchy of Croatia (which also expanded upon the territory of Sisak[26]) while Pannonia again became part of the Pannonian March, both of which vassals to East Francia.

[14] During the time of Kocel, Byzantine missionary Methodius was active in Lower Pannonia,[35] and to the same period is dated Pope John VIII's letter to uncertain dux Mutimir, commonly considered to be Mutimir of Serbia,[a] about the formation of the Diocese of Pannonia with the seat in Sirmium and which archbishop at Kocel's request was Methodius (see also Archbishopric of Moravia).

He participated in the Frankish–Moravian War, and in 895 or 896 Arnulf handed over Pannonia to him in order to secure the Frankish frontier against a new threat - the Hungarians who conquered Great Moravia.

[40][41] Following the rise of the Principality of Hungary in the mid 890s, and especially after Battle of Pressburg (907),[42] no further Slavic rulers were recorded in the regions of Lower Pannonia.

[27] In the mid 920s, Tomislav of Croatia expanded his rule to some Lower Pannonian territories, between Sava and Drava, adding them to the Croatian kingdom.

There has remained a general uncertainty and dispute over the borders between the Croatian and Hungarian states in the 10th and 11th century, with Croatian historian Ferdo Šišić and his followers assuming Tomislav of Croatia had ruled most of the area inhabited by Croats, including southern Pannonian regions (Slavonia), while the Hungarian historians Gyula Kristó, Bálint Hóman and János Karácsonyi thought the area between Drava and Sava rivers belonged neither to Croatia nor to Hungary at the time, an opinion that Nada Klaić said she would not preclude, because the generic name "Slavonia" (lit.

[42] With the continued growth of population, the formation of the church and administrative organization, including the founding of the diocese of Zagreb (1094), even after Croatia entered a personal union with the Kingdom of Hungary it retained partial autonomy having governor titled as Ban of Slavonia.

[47] Even after the Frankish defeat of Avars and the process of Christianization some pagan practices and rituals did not change, like a cemetery in rows, feasting at the funeral or steppe burial rite with horse and equipment.

[51] According to M. Guštin and L. Bekić, radiocarbon dating confirmed dating to late 6th and early 7th century, but although the Pannonian and near Alpine Slavs material culture had features of both Korchak and Penkovka-type, predominates Korchak-type with parallels in northern Slovenia, Austria and Hungary (among others from western Slovakia and Czechia's region of Moravia up to Ukraine, Poland, eastern Germany and Romania), indicating mostly migration to northern Croatia through the Moravian Gate between eastern Austria and western Hungary, but not excluding another migration wave from Lower and Middle Danube, upstream of the river Sava and Drava.

[59] According to the craniometrical measurements and archaeological findings early Croats did not initially settle in Lower Pannonia and their relationship with Pannonian Slavs was more political rather than ethnic.