Definition of Orthodoxy and its claim to apostolic succession.

The 19th and 20th centuries saw the Ottoman Empire crumble and the rise of modern nation-states in the Balkans. This led to the establishment of self-governing () national churches, such as the Romanian Orthodox Church, the Church of Greece, and the Serbian Orthodox Church. The Communist Crucible

The breaking point of 1054 and the Fall of Constantinople (1453).

Between the 4th and 8th centuries, the Church held seven Ecumenical Councils. These gatherings were crucial because they formulated Christian dogma and combated heresies like Arianism and Iconoclasm.

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The "Rum Millet" system under Ottoman occupation.

Tensions gradually mounted between the Greek-speaking East and the Latin-speaking West. Disagreements over papal supremacy and the Filioque clause (the insertion of "and the Son" into the Creed by the Western Church) led to the Great Schism in 1054. This event formally divided the Chalcedonian Church into the Roman Catholic Church and the Eastern Orthodox Church. Captivity and Expansion

Moscow as the "Third Rome" and the expansion of the Russian Church.