Final answer:
The Byzantine Empire could not sustain Justinian's conquests after his death due to financial strains from costly wars, renewed Germanic invasions, pressure from the Persian Empire, and the rise of the Islamic Rashidun state. These factors led to the loss of territories and decline of the empire's power and influence.
Step-by-step explanation:
Why Justinian's Conquests Did Not Endure After His Death
After the death of Emperor Justinian, the Byzantine Empire struggled to maintain its conquered territories due to several key factors. Justinian's campaigns had been extraordinarily costly, and the empire's finances were heavily burdened by the ongoing wars with the Persian Empire and the efforts to reclaim Western territories. These military endeavors led to the depletion of the treasury, making it difficult for his successors to sustain the military presence needed to hold onto the re-conquered lands.
The Germanic invasions resumed in the West, and the Persian Empire—under the Sassanid rule—continued its pressure on Byzantine territories in the East. The situation was further complicated by the emergence of the Islamic state of the Rashidun, which led to additional military conflicts and eventually the loss of vast territories previously under Byzantine control. Despite efforts to pay tributes and make peace, as in the case of the annual tribute to Persian king Khusro I, these measures were insufficient to maintain the empire's vast and overstretched boundaries in the long term.
The Byzantine Empire, while surviving past Justinian's era, became reduced in its territorial extent and power. It faced diminishing political and religious influence in the face of emerging powers, signaling the decline of what was once a formidable empire with far-reaching boundaries.