The declaration of first-rate unity of the elements of the Byzantine Empire is the unfolding of the Black Plague.
What is the Ottoman Empire?
The Ottoman Empire became an empire that managed plenty of Southeast Europe, Western Asia, and Northern Africa between the fourteenth and early twentieth centuries.
It is based on the stopover of the thirteenth century in northwestern Anatolia within the metropolis of Söüt (modern Bilecik Province) by the Turkoman tribal chief Osman I.
So, from the above rationalization, it's clear that alternative B, the unfolding of the Black Plague, is the precise alternative.
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