Which external enemy proved to be the greatest continuing threat to the byzantine empire in the 15th century? the abbasids the goths the romans the turks

In the 15th century, the upcoming Turkish power has already grown. Turkey was a threat to the Byzantine Empire, as well as to the countries east of Byzantium towards the Balkans. At that time, the once mighty Byzantine Empire was greatly reduced to almost the area around Constantinople. With the fall of the capital city of 1453, finally Byzantium fell under the rule of the Turks.

The answer is: Turks.

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