The Roman Empire used to cover the entire Mediterranean basin at the noon of its glory. Yet on its ruins, from its ashes several realms emerged. Most widely, the Rhomaic empire was seen as the most true successor of the original Senatus populusque Romanum. While reduced to the former Pretorian prefectures of Macedoniae, Asian, Pontus and southern half of Thraciae, as well as portions of coastal Italy here and there(1). The Isaurian dynasty (2), who rules the empire during the larger part of the 8th century. The reign of Leo III was marked by several events: on one hand was a further colonization of northwestern Anatolia by Slavic clans, in the legal dimension, ancient Roman law in the form of Codex Iustinianus has been revised into a new code of law called the Ecloga. In its effects, this caused the end of serfdom within the empire, and serfs became free tenants.
In religious policy, the new emperor favored a rather strict view regarding the veneration of icons. While not yet official policy with the force of law, any veneration of icons was now frowned upon, and the Emperor aims to dissuade his subjects from such customs. His rather strict view on religion was in contrast to his policy of persecution of other strict sectarian movements such as Montanists. Jews were force-baptized. The conflict with the Pope in Rome was deepened by the Emperor transferring Calabria, Basilicata and Apulia, as well as Sicily and Ilyricum from the authority of Rome to the Patriarchate of Constantinople.
The next Emperor, Constantine V., was concerned with securing the northern and southeastern borders of the Empire (3). On the Syrian front, important advances were made - the conquest of the entire region of Cilicia ,of Edessa and the city of Antioch with environs. There, he could once more count upon the Antiochian Greeks, who once more sought support from Constantinople. In the north, the Rhomaic empire from its bases in the Axios valley (4) sought to regain some of the lost territories even further northwards. They managed to regain Naissos (5) and Serdica (6). In Italy, however, the Lombards conquered Ravenna, which were a center of Rhomaic administration in the area. This, however, was connected with Rome, and this stripe of land (8) cut the Lombard state in two, disallowing effective control of the south of the country from the Lombardic capital at Pavia
In the south however, the remaining areas of Tafirca, roughly corresponding to late roman provinces of Zeugitana and Byzacena, were reincorporated into the empire
Leo IV and Constantine VI lacked any strong landmark of their rule. However, in the later years of the Isaurian dynasty, the policy regarding the venreation of icons were changed, and such practice was allowed more openly (yet its staunch critics could be found within parts of Anatolia).
The remaining parts of the former East Roman Empire had historical traditions of its own , and did not aim to replicate Roman symbolism. Such was the case particularly in Egypt, which had a history far longer than Rome. Yet in the west, there were numerous states that aimed to claim the legacy of Rome as theirs - most notably, the two most important competitors for such a title could be found in Hispania and Gallia.
These two were most advanced, yet soon they faced the problems of administering a larger realm and the problems of succession. The Frankish custom of dividing the realm amongst the heirs upon succession proved disastruous to the stablity of administration and royal majesty as well. The Visigoths adopted a custom of electing the king; the problems of local administration were to be solved by devolution - a concept that is sometimes described as protofeudalism; in contrast to the "real" feudalism in the Hispanic variant, it were public oaths of loyalty to the liege, not individual ones as in the later variant. Yet in Hispania, and Gaul itself a change of society resulted in a move out of the city, out of the urban center to the castle. Such a change was quite a natural development in Hispania and Gallia, more so in Germany, for the areas were not densely populated during Roman times either. The climate allowed for a dispersed population, and agriculture was more effective in such a manner. A castle was thus a seat of local administration, the seat of the noble who collected tax from the rural populace, who would in times of danger seek refuge in the fortified place.
The Iberian peninsula, formerly the Roman Pretorian prefecture of the Hispanies was now controlled by the Visigothic kingdom, who controlled also the coastal strip of Septimania, the last parts of the former Visigothic hold in Viennensis (9). The aim of the later Visigothic kings was to reclaim Tolosa, the former capital of their kingdom from the Franks. They aspired to be recognized as emperors of the west, and the Pope used to address the Visigothi kings as "imperator Hispaniae et rex Gothorum"
Francia by this time was dominated by the mayors, and role of the Merovingian dynasty was merely symbolic. The ruling majordomi campaigned to establish Frankish hegemony over western Europe by subduing neighboring Germanic tribes - Alamanni, Bavarians, Frisians. Aquitania, a region roughly between the Loire and the Pyrennees was long hoping to separate itself from Frankish rule. This effort to weaken their major rival rival was sponsored and supported by Visigoths and Lombards as well.
(1) This althist Byzantium is comparatively stronger to its OTL counterpart, due to including all of Greece, Macedonia , Albania as well as Upper Thrace within its borders.
(2) Maybe the original identity of the persons was digfferent. For some reason, most my laziness or lack of creativity, similar dynasties arise in places and times, as they would have in OTL. Yet, due to butterflies, their actions are somewhat different
(3) Divergent from OTL. In OTL the Emperor was concerned mainly with the Balkans. In ATL, with Balkans secured, major focus is in Syria
(4) Vardar Macedonia
(6) Niš,Serbia
(7) Sofija, Bulgaria
(8) similar to the borders of Papal States
(9) Roughly corresponding to Occitania