In the latter half of the 20th century, train travel was in decline because of competition from international air and bus travel. The last train called the Orient Express—far from luxurious and a mere shadow of its glorious former self—was removed from the rails and the schedules in 1977.
The Yugoslav wars from 1991 to 2001 made train travel in the Balkans not merely uncertain and uncomfortable, but mortally dangerous.
After the wars, in the early years of the new millennium, Balkan train travel was hardly worthy of consideration for international travelers. I received reports from travelers who rode the rails through Serbia and Bulgaria, and the reports were not good.
In recent years, however, the governments of the Balkan countries and Turkey have invested in their railroads, and train travel between Turkey and Europe through the Balkans is again a viable, interesting, and at least moderately comfortable way to go.