Although having developed a science of war, as Runciman observes, Byzantium was not a military state. Obliged in a constant war, no matter how powerful it might have been, no matter how well it knew to combat, obviously it could not resist a global attack – from the East, the South, the North, and even from the West, from the Christian nations. That acknowledged, it is no wonder that Byzantium fell, but that it resisted for 11 centuries.
Beyond these and above all explanations one might give, we can not understand Byzantium if we imagine it to be a ‘nation’. With every province that was lost, especially of the western provinces that signified the start of the empire in the older Rome, Byzantines received not only a political wound, but even more seriously a wound in their soul, in their ecumenical nature. A Byzantium that was getting identified with Greeks, due to the loss of eastern and western provinces, was not losing just power, but its very nature.