Final answer:
The decline of the Byzantine Empire was caused by invasions and plagues.
Step-by-step explanation:
The two main reasons for the decline of the Byzantine Empire were invasions and plagues. Invasions by various groups such as the Seljuks and the Ottomans weakened the empire and eventually led to its downfall. Plagues, such as the Black Death, also caused widespread death and economic disruption, further contributing to the empire's decline.
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