How much power did the controller of naval straits such as Bosporus exert over the trade through the strait itself? Would they be able to impose significant blockades against merchant ships of opposing powers?
I wrote a relevant post before in When and how did straits like those of Gibraltar, Bosporus and Denmark become an unpassable obstacle for ships that were rejected passage?.
In short, it was not until the end of the Middle Ages [15th century] that the polity controlling the land part of the strait generally had enough means to cut the total traffic off, without the help of reasonable size of fleet in medieval Europe.