Answer:
The correct answer is 'Attacks by Christian Crusader from Europe'
Explanation:
The Byzantine Empire did not officially fell until the capture of Constantinople by the Ottoman forces. However, by the time, it was just a shadow of it's formal self and was very weak.
While in the 10th century, the city was known for it's wealth and opulence, by the time of the Fourth Crusaders, it's economy had deteriorate completely and lead to its eventual demise.
Since the first crusaders came from Europe, they had a constant friction with the Byzantine's. Many crusaders formed their own small kingdoms from the land they captured within the Empire.
