In bringing about the fall of the Turkish, Austrian, and Russian empires, World War I provoked significant changes in the structures of the Eastern Orthodox Church. On the western borders of what was then the Soviet Union, in the newly born republics of Finland, Estonia, Latvia, and Lithuania, the Orthodox minorities established themselves as autonomous churches. The first three joined the jurisdiction of Constantinople, and the Lithuanian diocese remained nominally under Moscow. In Poland, which then included several million Belorussians and Ukrainians, the ecumenical patriarch established an autocephalous church (1924) over the protests of Patriarch Tikhon. After World War II the Estonian, Latvian, and Lithuanian autonomies were again suppressed, and in Poland the Orthodox church was first reintegrated to the jurisdiction of Moscow and later declared autocephalous again (1948).

In the Balkans changes were even more significant. The five groups of Serbian dioceses (Montenegro, the patriarchate of Karlovci, Dalmatia, Bosnia-Herzegovina, and Serbia) were united (1920–22) under one Serbian patriarch, residing in Belgrade, the capital of the new Yugoslavia. Similarly, the Romanian dioceses of Moldavia-Walachia, Transylvania, Bukovina, and Bessarabia formed the new patriarchate of Romania (1925), the largest autocephalous church in the Balkans. Finally, in 1937, after some tension and a temporary schism, the patriarchate of Constantinople recognized the autocephaly of the church of Albania.

After World War II communist regimes were established in the Balkan states. There were no attempts, however, to liquidate the churches entirely. In both Yugoslavia and Bulgaria church and state were legally separated. In Romania, paradoxically, the Orthodox church remained legally linked to the communist state. With its solid record of resistance to the Germans, the Serbian church was able to preserve more independence from the government than its sister churches of Bulgaria and Romania. Generally speaking, however, all the Balkan churches adopted an attitude of loyalty to the new regime, according to the pattern given by the patriarchate of Moscow. At that price, they could keep some theological schools, some publications, and the possibility of worship. This was also the situation of the Orthodox minority in Czechoslovakia, which was united and organized into an autocephalous church by the patriarchate of Moscow in 1951. Only in Albania did a communist government announce the total eradication of organized religion, following its cultural revolution of 1967.

Among the national Orthodox churches, the Church of Greece is the only one that preserved the legal status it acquired in the 19th century as the national state church. As such, it was supported by the successive political regimes of Greece. It could also develop an impressive internal mission. The Brotherhood Zoe (“Life”), organized according to the pattern of Western religious orders, was successful in creating a large system of church schools.

The communist governments throughout eastern Europe collapsed during the late 1980s and early 1990s, effectively dissolving state control over churches and bringing new political and religious freedoms into the region. In the early 1990s Czechoslovakia and Yugoslavia were divided into countries that reflected older ethnic identities. In each case, one Orthodox church continued to have jurisdiction. The Czech and Slovak Orthodox Church has jurisdiction over the Czech Republic and Slovakia (both of which became independent states in 1993). The Serbian Orthodox Church has jurisdiction over the countries that once constituted Yugoslavia: Serbia, Croatia, Bosnia and Herzegovina, North Macedonia, and Montenegro. The Albanian Orthodox Church was reconstituted in 1992 with the appointment by the ecumenical patriarchate of a Greek primate. In 2019 the Orthodox Church of Ukraine was granted independence from the Russian Orthodox Church, a move that caused tensions between the patriarchate of Moscow and the Ecumenical Patriarchate of Constantinople, which approved of the split.

The Eastern Orthodox Church in the Middle East

As a result of the Greco-Turkish War, the entire Greek population of Asia Minor was transferred to Greece in 1922. The Orthodox under the immediate jurisdiction of the ecumenical patriarchate of Constantinople were thus reduced to the Greek population of Istanbul and its vicinity. This population was reduced to a few thousand by the early 21st century. Still recognized as holding an honorary primacy among the Orthodox churches, the ecumenical patriarchate also exercises jurisdiction over several dioceses of the “diaspora” and, by consent of the Greek government, over the Greek islands. The impressive personality of Patriarch Athenagoras I (1948–72), who was succeeded by Dimitrios, contributed to its prestige on the pan-Orthodox and ecumenical levels. Beginning in 1962, the patriarchate convened pan-Orthodox conferences in Rhodes, Belgrade, Geneva, and other cities and began preparations for a “Great Council” of the Eastern Orthodox Church.

Together with the ecumenical patriarchate, the ancient sees of Alexandria, Antioch, and Jerusalem are remnants of the Byzantine imperial past, but under the present conditions they still possess many opportunities of development: Alexandria as the centre of emerging African communities (see below The Orthodox diaspora and missions); Antioch as the largest Arab Christian group, with dioceses in Syria, Lebanon, and Iraq; and Jerusalem as the main custodian of the Christian holy places in that city.

The two ancient churches of Cyprus and Georgia, with their quite peculiar history, continue to play important roles among the Orthodox sister churches. Autocephalous since 431, the church of Cyprus survived successive occupations, and often oppressions, by the Arabs, the Crusaders, the Venetians, the Turks, and the English. Following the pattern of all areas where Islam was predominant, the archbishop is traditionally seen as the ethnarch of the Greek Christian Cypriots. Archbishop Makarios also became the first president of the independent Republic of Cyprus in 1960. The church of Georgia, isolated in the Caucasus in a country that became part of the Russian Empire in 1801, is the witness of one of the most ancient Christian traditions. It received autocephaly from its mother church of Antioch as early as the 6th century and developed a literary and artistic civilization in its own language. Its head bears the traditional title of “Catholicos-Patriarch.” When the Russians annexed the country in 1801, they suppressed Georgia’s autocephaly, and the church was governed by a Russian exarch until 1917, when the Georgians reestablished their ecclesiastical independence. the Georgian church was fiercely persecuted during the 1920s but survives to the present day as an autocephalous patriarchate.

Orthodoxy in the United States

The first Orthodox communities in what is today the continental United States were established in Alaska and on the West Coast, as the extreme end of the Russian missionary expansion through Siberia (see above The church in imperial Russia). Russian monks settled on Kodiak Island in 1794. Among them was St. Herman (canonized 1970), an ascetic and a defender of the indigenous people’s rights against ruthless Russian traders. After the sale of Alaska to the United States, a separate diocese “of the Aleutian Islands and Alaska” was created by the Holy Synod (1870). After the transfer of the diocesan centre to San Francisco and its renaming as the diocese “of the Aleutian Islands and North America” (1900), the original church establishment exercised its jurisdiction over the entire North American continent. In the 1880s it accepted back into Orthodoxy hundreds of “Uniate” (Eastern rite) parishes of immigrants from Galicia and Carpatho-Russia, particularly numerous in the northern industrial states and in Canada. It also served the needs of immigrants from Serbia, Greece, Syria, Albania, and other countries. Some Greek and Romanian communities, however, invited priests directly from the mother country without official contact with the American bishop. In 1905 the American archbishop St. Tikhon (the future patriarch of Moscow) presented to the Russian synod the project of an autocephalous church of America, whose structure would reflect the ethnic pluralism of its membership. He also foresaw the inevitable Americanization of his flock and encouraged the translation of the liturgy into English.

These projects, however, were hampered by the tragedies that befell the Russian Orthodox Church following the Russian Revolution. The administrative system of the Russian church collapsed. The non-Russian groups of immigrants sought and obtained their affiliation with mother churches abroad. In 1921 a “Greek Archdiocese of North and South America” was established by the ecumenical patriarch Meletios IV Metaxakis. Further divisions within each national group occurred repeatedly, and several independent jurisdictions added to the confusion.

American Orthodoxy challenged the feasibility of preserving the ethnic identity of the national churches, which had characterized Orthodoxy in Europe and the Middle East. A reaction against this chaotic pluralism manifested itself in the 1950s. More cooperation between the jurisdictions and a more systematic theological education contributed to an increased desire for unity. A Standing Conference of Canonical Orthodox Bishops in the Americas (SCOBA) was established in 1960 in order to provide administrative unity amid jurisdictional confusion. In 1970 the patriarch of Moscow, reviving Tikhon’s project of 1905, formally proclaimed its diocese in America (which had been in conflict with Moscow since 1931 on the issue of loyalty to the Soviet Union) as the autocephalous Orthodox Church in America (OCA), which had no administrative connections abroad. However, the ecumenical patriarchate of Constantinople protested this move, turned down a request for autonomy presented by the Greek archdiocese (the largest single Orthodox body in the United States), and reiterated its opposition to the use of English in the liturgy. Meanwhile, the American archdiocese of the Antiochian Orthodox Church was granted self-rule (though not full autocephaly) in 2003 and later incorporated into itself the Evangelical Orthodox Church, a group of former Evangelicals who embraced Orthodoxy. Led by Peter Gillquist, it operates as the Antiochian Evangelical Orthodox Mission (AEOM) and promotes the unity of Orthodox Christians in America.