The history of the Byzantine Empire starts with the adoption of Christianity and foundation of Constantinople by Constantine I the Great. The final division between East and West in the Roman Empire came after the death of Theodosius I (395) and the accession of his elder son, Arcadius, in the East marked its supremacy. Both parts now suffered the attacks of barbarians, Goths, Vandals or Huns, but the East with its greater resources generally succeeded in deflecting their attacks westwards, where the last emperor was deposed in 476. The East was also troubled by an intermittent war with the Persians, and regular religious conflicts. The most serious were the heresies of the Nestorians and Monophysites that found many adherents in Egypt, Syria and Armenia. The emperors tried to find a compromise doctrine but only managed to alienate all parties, in particular the Papacy. Peace only came when these areas were lost to the Arabs. Nevertheless, the Empire was rich enough for Justinian I (527-65) to embark on grand schemes of reconquest and building, but after his death the situation rapidly became critical. He had left the economy exhausted and successors suffered the consequences. The newly won provinces of Italy and Spain were not secure and soon lost. The Balkans was overrun by Avars and Slavs, and in the east, where disaffection and heresy were rife, the Persian war resumed with particular violence. Heraclius (610-41) for a time remedied the military situation, only to see Egypt and Syria fall at once to the Arabs whose advance seemed irresistible. It was in fact checked at Constantinople itself, where the victories of Constantine IV (678) and Leo III (718) over the besieging Arab forces can be compared with that of Charles Martel in France.
The period from Heraclius to Leo III (717-40) is when the Empire took on its specifically Byzantine and medieval characteristics. Territorially it was reduced to South Italy and Sicily, the Balkan peninsular, and Asia Minor. The loss of the Latin and Catholic west and the Monophysite Syrians and Egyptians left it Greek and Orthodox. Many of the Roman institutions vanished too: the cities, once so prominent, became forts or perished, as did their municipal traditions. Instead of the estates of the Late Roman Empire, there emerged a free peasantry. In the provinces the division of civil and military power was replaced by the military government in new units called themes. The central armies were largely broken up, and distributed round these, and recruited from the new class of peasants. In the 8th and 9th centuries the military situation stabilized. War with the Arabs in the east became more an affair of raids and counter raids, and the Byzantines had several successes. In the Balkans, though Slav irruptions ceased and Byzantine authority began to expand, the Bulgars established themselves south of the Danube and presented a potent threat. Italy however was left to the Lombards. Consequently the Popes turned to the Franks for protection, and in 800 the Byzantine theory of universal empire was formally shattered by the coronation of Charlemagne as ‘Roman Emperor’. Sicily too was gradually lost to the Arab. The chief feature of this era was Iconoclasm, which was not a purely religious phenomenon, but had distinct political and social aspects. Proclaimed by Leo III (730), the controversy lasted until 842, with a break from 787 to 815, when Orthodoxy was restored by Irene. From the first it caused opposition, in Byzantium and in the West, which soon grew bitter.
The next period was the golden age of the Byzantine Empire. In the east its armies went from strength to strength, and under Nicephorus II Phocas and John I Tzimisces (969-976) the war took on the atmosphere of a crusade. In the Balkans, Byzantine control was finally affirmed, despite repeated and costly wars with Bulgaria. The Russians too were brought within the imperial orbit. Relations with the West continued to deteriorate: there were several clashes with the Papacy and the Germans. Within the Empire, the “thematic system” of provincial government had become standard, but as offensive wars grew commoner, centralized armies re-emerged and so did the division between civil and military functions. The bureaucracy gained in power. Trade and economy prospered and the towns and cultural activities revived. However, after the death of Basil II (1025), this system began to decay. The peasantry, the basis of government revenue, was being impoverished, and falling prey to landowners who were able to extort privileges from the emperors. Extravagance and mismanagement weakened imperial finances and the coinage was debased. Overconfidence lead to the neglect of the army and defenses. There was also growing strife between the bureaucratic establishment at Constantinople and the military one of provincial landowners. Eventually a representative of one of the latter, Alexius I Comnenus (1081-1118) seized power. By then the survival of the Empire was in doubt, for it was caught between Turkic tribes from the east and Normans from Italy; the frontiers were only stabilized when much had been lost. Alexius I Comnenus reformed the administration and finances, but could not prevent regular revolts. In 1081 he deposed Nicephorus III. He came from one of the most distinguished Byzantine aristocratic land-owning families and his accession symbolized their domination of the Empire. His first task was to save the Empire, for Turkic tribes had overrun Anatolia, Pechenegs the Balkans, and the Normans were invading Albania. Allied with Venice, in exchange for very extensive trading concessions, he repelled the Normans (1085 and 1108). He destroyed the Pechenegs in 1091. Against the Turkic tribes he called for Western support, and these appeals helped to stimulate the First Crusade (1097). The Crusaders did help clear western Asia Minor although their passage caused severe problems, and conflicts arose when they began to occupy former Byzantine territory in the Levant. Alexius Comnenus also reformed the taxes and the coinage, which had become very debased under his predecessors, and reconstituted the army and administration. He was, however, unable to prevent an epidemic of conspiracies and revolts, although he survived them all.
Nonetheless the Empire prospered, until under the weak Angeli (1185-1204) it collapsed altogether. The Turkmens and Bulgarians again advanced, and the Empire began to fragment. Mutual hostility between it and the West sharpened, in particular during the Crusades, and was encouraged by the dominance the Italians took in trade. This lead to the sack of Constantinople by the Fourth Crusade in 1204, and the creation of a Latin Empire. Venice was the main beneficiary; most of the other conquests proved ephemeral, and within two decades had been lost. Constantinople itself was recaptured by the Byzantines in 1261. The Byzantine Empire never fully recovered.
Three successor empires emerged-Trebizond , Epirus and Nicea, which from the weakest position became the most powerful. There a prosperous base was established from which Epirus and the Latin Empire were reconquered. In this period the Byzantine Empire came to be dominated by the nobility and took on a form similar to the feudal Latin Empire. Separatist tendencies flourished, and spread within the imperial family, and the country was repeatedly ravaged by civil wars. The arts and scholarship however flourished and they were an important factor in stimulating the Renaissance.
After 1261 the Empire’s external situation grew increasingly severe. The immediate threats from the West were warded off by Michael VIII Palaeologus (1258-82); instead the Empire looked there for aid against the Turks. To further their claims the emperors set up talks between the Orthodox and Catholic churches. A union was finally negotiated at Florence in 1439, but was rejected by most Byzantines. However no significant help materialized, and the Crusades of Nicopolis (1396) and Varna (1444) were miserably defeated by Ottomans. The Empire also became commercially dependent on Venice and Genoa, and was usually the main casualty in their frequent conflicts. In the Balkans, the Serbian Empire eclipsed the Bulgarians, but, there as in Asia the Ottoman Turks swept all before them. The Empire’s Asian provinces were neglected and lost; Nicea was taken in 1331, and in 1354 the Ottomans crossed into Europe. By 1389 they had subdued Serbia and Bulgaria, and the Byzantines had had to acknowledge their sovereignty. Sultan Bayezid were defeated by Turco-Mongol emperor Tamerlane (1402) in the battle of Angora (Ankara), but the Ottomans after 10 years completely recovered. The final assault on Constantinople was led by Ottoman sultan Mehmed II in 1453. The city fell on 29 May and the Byzantine Empire came to an end.