By about 15 million years ago plate collisions had shut the seaways of the Tethys and created mountain barriers in the Balkans and on both sides of Iran. However, with major rivers like the Volga and Danube draining into the former northern arm of the Tethys, the water had to go someplace.
Turkey, Greece, and Iran are small pieces of continental crust that are being crunched by the convergence of Africa and Eurasia. 20 million years ago the plates looked something like this. There were still remnants of the Tethys. Columbus wouldn't have needed to sail west to reach Asia, and there would have been no need for a Suez Canal.

Greece, Turkey, and Iran are drawn in their present shapes, but the reality is they are all mosaics of small pieces and nobody has a clear idea exactly what they looked like. They were probably originally attached to Africa, but the details are still unknown.
The drainage divides northward to the Baltic are only about 160 meters (500 feet) above sea level, so f