Complex sentence: Since the Balkans fell under Ottoman rule, the Bulgarian word has been used exclusively as another name of Constantinople, because in the vernacular of the Balkan Slavs the Ottoman sultans were called tsars Софроний Врачански.
Split into simpler sentences: Since the Balkans fell under Ottoman rule, the Bulgarian word has been used exclusively as another name of Constantinople. In the vernacular of the Balkan Slavs the Ottoman sultans were called tsars Софроний Врачански.