Orthodoxy is currently in a state of internal rupture, and it is a live event rather than a historical one.
In October 2018 the Moscow Patriarchate broke communion with Constantinople after the Ecumenical Patriarch announced his intention to recognise an independent Ukrainian church. On 5 January 2019 the tomos of autocephaly for the Orthodox Church of Ukraine was signed. Moscow regards the act as an invasion of its canonical territory and the new body as uncanonical; Constantinople regards the granting of autocephaly as its own prerogative and holds that Ukraine was never permanently transferred to Moscow in the first place.
The communion has not divided cleanly. The churches of Greece, Alexandria and Cyprus recognised the new Ukrainian church across 2019 and 2020, and Moscow broke communion with the recognising hierarchs in turn. Most other autocephalous churches have declined to take a public position, which leaves large parts of Orthodoxy in the awkward position of being in communion with two bodies that are not in communion with each other. The Russian invasion of Ukraine in 2022 hardened everything: the Moscow patriarch's public support for the war drove even the Ukrainian church that had remained under Moscow to declare its independence, and prompted sanctions and legal restrictions on Moscow-linked structures.
Worldwide Eastern Orthodox numbers are usually estimated around 220 million, the second-largest Christian body after the Catholic Church. The great majority of those are in Russia, Ukraine, the Balkans, Georgia and Romania, which is why a quarrel over Ukraine is not a regional matter but a fight over the demographic centre of the communion.