Orthodoxy and Nationalism
Unfortunately, it is a common misconception to link Orthodox Christianity with nationalism.
The French Revolution paved the way for the modern nation-state, and with it came several revolutionary ideas that brought the decline and fall of the Ottoman Empire.
Starting from the 18th century onward, romantic nationalism was carried to Eastern Europe that caused the disintegration of the Ottoman millet system. Because those living under the Ottoman Empire were bound by religious, linguistic, and cultural affiliations, citizenship and ethnic origin were considered relatively unimportant.
Under this system, religious hierarchs such as the Greek Orthodox Patriarch of Constantinople reported directly to the Sultan of the Ottoman Empire. The struggle for political freedom erupted under these Christian hierarchs, first by the Serbians and then by the Rhomaioi (Greeks), and this was followed by a wave of national awakening across the entire empire.
From the fourth century, a Christianized Roman (Greek) culture had developed that the Turks had not been able to destroy. At the same time, it is important to note that nationalism has had little to nothing to do with Orthodoxy and that it is the product of secular philosophies that had developed in Western Europe.
Many Christian ideas, as they pertain to spiritual salvation, have historically often at odds with secular ideologies such as nationalism. For example, when Greece first became independent it had a German monarch, German architecture, and the German idea of Church-State relations. The Orthodox Church of Greece was established as autocephalous, without reference to Constantinople, and where the Patriarchs had initially opposed it due to Ottoman pressure in Constantinople.