The Serbs and Croats are thought by some authorities to have originated as Sarmatian elites ruling Slav populations. They were commissioned by the Byzantine emperor Heraklios in 627 to drive the Avars out of western Illyricum and settle there on condition that they became Orthodox Christians. They quickly merged with their new Slav subjects. The Serbs became nominally independent of Byzantium in 820, but Muslim raiders caused second thoughts and they returned to being increasingly rebellious subjects until 1180. The Croats accepted the rule of Charlemagne after the defeat of the Avars in 796 and became Catholic, but later rebelled, gaining independence from both Franks and Byzantines in 879. They were conquered by Hungary in 1089. Serbs and Croats shared a language, mutual dislike and a love of ambushes. The military repute of the Serbs was as fiercely-charging lancers and deadly archers, that of the Croats as axemen. Reference: Armies of Feudal Europe 1. Heath.
— Serbian Army 627 AD - 1180 AD
III/13 — AVAR 553 AD - 826 AD
III/14 — EARLY BULGAR 558 AD - 1018 AD
III/17 — MAURIKIAN BYZANTINE 575 AD - 650 AD
III/1 — EARLY SLAV 476 AD - 1218 AD
III/26 — EARLY SERBIAN OR CROATIAN 627 AD - 1180 AD OR 1089 AD
III/29 — THEMATIC BYZANTINE 650 AD - 963 AD
III/65 — NIKEPHORIAN BYZANTINE 963 AD - 1042 AD
III/68 — EARLY HUNGARIAN 997 AD - 1245 AD
III/76 — KONSTANTINIAN BYZANTINE 1042 AD - 1073 AD
IV/1 — KOMNENAN BYZANTINE 1071 AD - 1204 AD
— Croatian Army 627 AD - 1089 AD
II/76 — KOGURYO KOREAN 300 AD - 668 AD
III/13 — AVAR 553 AD - 826 AD
III/17 — MAURIKIAN BYZANTINE 575 AD - 650 AD
III/1 — EARLY SLAV 476 AD - 1218 AD
III/26 — EARLY SERBIAN OR CROATIAN 627 AD - 1180 AD OR 1089 AD
III/28 — CAROLINGIAN FRANKISH 639 AD - 888 AD
III/29 — THEMATIC BYZANTINE 650 AD - 963 AD
III/65 — NIKEPHORIAN BYZANTINE 963 AD - 1042 AD
III/68 — EARLY HUNGARIAN 997 AD - 1245 AD
III/73 — COMMUNAL ITALIAN 1029 AD - 1320 AD