Final answer:
The Byzantine Empire's stability was largely due to its effective bureaucracy which maintained order within the government, complemented by aggressive diplomacy and periods of economic prosperity and military strength.
Step-by-step explanation:
The Byzantine Empire's long-term stability can be most attributed to its effective bureaucracy. Notably, the imperial bureaucracy wielded substantial power, with provincial elites sending their sons to Constantinople to study and secure government positions. Despite practices such as bribery and nepotism, the bureaucracy maintained order, particularly under competent emperors. Byzantium's bureaucracy was likened to the class of Egyptian scribes, preserving government coherence even amidst individual incompetence or palace intrigue. Moreover, Byzantium's bureaucratic structure was critical in managing external threats and internal challenges, contributing to the empire's resilience over centuries.
Other factors that supported Byzantine stability included the diplomatic strategies, exemplified by the "Bureau of Barbarians" which played a role in international relations by gathering intelligence and preparing diplomats for missions. Furthermore, efforts to manage the economy and military, especially during the Macedonian dynasty, provided periods of stability and cultural prosperity, as seen in the Macedonian Renaissance's influence on Italian art. However, the military prowess and economic prosperity were subject to fluctuation and ultimately singularly could not ensure long-term stability.