The land border between Bulgaria and Turkey currently serves as the southeastern frontier of the European Union, and it also Turkey’s most vulnerable one. Whereas Turkey’s eastern borders are separated from the majority of its population by over a thousand kilometres of hills and mountains, the distance between Istanbul and the Turkish-Bulgarian border is less than 200 kilometres, and the terrain is relatively flat the whole way.
Not incidentally, it was from the area that is today Bulgaria that the Romans conquered Byzantium (today’s Istanbul) in 173 BC, and that European forces conquered Constantinople (also today’s Istanbul) during the Fourth Crusade in 1204 AD. In fact the Turks themselves conquered Constantinople from this direction, in 1453 AD, though in their case they approached the city from both east and west simultaneously.
If Turkey were to formally or informally dominate even just the southern half of Bulgaria, as its Ottoman predecessors did for nearly five hundred years between 1396 and 1885, the distance between its western border and Istanbul would double. Even more important, Turkey would then be able to anchor itself on the Balkan Mountains instead of on the flat lowlands which currently comprise much of the border between the two countries.
This would give Turkey a defensible buffer in the north, while also allowing it to outflank any theoretical threat that might emerge on its border with Greece, its long-time rival, which like Bulgaria has a border located near to Istanbul. In addition, it would allow Turkey to prevent the Russians from circumventing the Turkish Straits by sending their goods to the Mediterranean by way of Bulgaria and Greece. Obviously the Turks would find such a state of affairs to be quite beneficial, all other things being held equal.
This is important, because Turkey could probably dominate Bulgaria if it wanted to, unless the Bulgarians were receiving support from an outside power like the United States, Russia, or the Europeans. Turkey is a much larger and wealthier country than Bulgaria is. Its gross domestic product is thought to be 20 times larger than Bulgaria’s, and its population is more than 10 times larger than Bulgaria’s. There is, in addition, a large Turkish diaspora living within Bulgaria, accounting for more than 10 percent of the country’s total population and more than half of the population in two of its 28 provinces.
You can read the full article here.