Theme system in the context of "Praetorian prefecture"

The Byzantine economy was among the most robust economies in the Mediterranean and the world for many centuries. Constantinople was a prime hub in a trading network that at various times extended across nearly all of Eurasia and North Africa. It could be argued that up until the 7th century, the Eastern Roman Empire had the most powerful economy in the world. The Arab conquests, however, would represent a substantial reversal of fortunes contributing to a period of decline and stagnation. The Byzantine state restructured its administrative and fiscal systems, introducing the theme system, which organized land and military service in a way that ensured both local defense and agricultural productivity. Rural life revived as new lands were brought under cultivation, and local economies became more self-sufficient, reducing dependence on long-distance trade that had been curtailed by the loss of eastern territories. By the 9th and 10th centuries, the empire experienced a notable resurgence: agricultural output increased, population levels rose, and the circulation of coinage expanded once again. However, by the 12th and 13th centuries, the economic balance began to shift. Western maritime republics such as Venice and Genoa gradually overtook Byzantine merchants, largely due to the tax exemptions and trading privileges granted to them under the Komnenian emperors. This process accelerated after the Fourth Crusade and the establishment of the Latin Empire, during which Venetian traders gained control over key ports and commercial networks once held by the Byzantines. The Byzantines continued to face economic challenges during the Palaiologan era until its fall in 1453.

One of the economic foundations of the empire was trade. The state strictly controlled both the internal and the international trade. Constantinople remained the single most important commercial centre of Europe for much of the Medieval era, which it held until the Republic of Venice slowly began to overtake Byzantine merchants in trade; first through tax exemption under the Komnenoi, then under the Latin Empire.

The Byzantine army was the primary military body of the Byzantine armed forces, serving alongside the Byzantine navy. A direct continuation of the Eastern Roman army, shaping and developing itself on the legacy of the late Hellenistic armies, it maintained a similar level of discipline, strategic prowess and organization. It was among the most effective armies of western Eurasia for much of the Middle Ages. Over time the cavalry arm became more prominent in the Byzantine army as the legion system disappeared in the early 7th century. Later reforms reflected some Germanic and Asian influences—rival forces frequently became sources of mercenary units, such as the Huns, Cumans, Alans and (following the Battle of Manzikert) Turks, meeting the Empire's demand for light cavalry mercenaries. Since much of the Byzantine military focused on the strategy and skill of generals utilizing militia troops, heavy infantry were recruited from Frankish and later Varangian mercenaries.

From the 6th to the 12th centuries, the Byzantine army was among the most powerful and effective military forces in the world – neither Middle Ages Europe nor (following its early successes) the fracturing Caliphate could match the strategies and the efficiency of the Byzantine army. Restricted to a largely defensive role in the 7th to mid-9th centuries, the Byzantines developed the theme system to counter the more powerful Caliphate. From the mid-9th century, however, they gradually went on the offensive, culminating in the great conquests of the 10th century under a series of soldier-emperors such as Nikephoros II Phokas, John Tzimiskes and Basil II. The army they led was less reliant on the militia of the themes; it was by now a largely professional force, with a strong and well-drilled infantry at its core and augmented by a revived heavy cavalry arm. With one of the most powerful economies in the world at the time, the Empire had the resources to put to the field a powerful host when needed, in order to reclaim its long-lost territories.

The subdivisions of the Byzantine Empire were administrative units of the Eastern Roman or Byzantine Empire (330–1453). The Empire had a developed administrative system, which can be divided into three major periods: the late Roman/early Byzantine, which was a continuation and evolution of the system begun by the emperors Diocletian and Constantine the Great, which gradually evolved into the middle Byzantine, where the theme system predominated alongside a restructured central bureaucracy, and the late Byzantine, where the structure was more varied and decentralized and where feudal elements appeared.