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Russia's effort to keep Ukraine under its thumb prompted a revolution in 2014 and a war that has claimed more than 10,000 lives.

It also prompted, on Monday, what may be one of the most serious splits in Christendom since the Great Schism between Rome and Constantinople in 1054 and the Protestant Reformation 500 years ago. This new crisis has deep historical roots, and could shape religious and secular ties among many countries for years to come, Nikos Konstandaras, a columnist at the Greek newspaper Kathimerini, wrote in an article for the New York Times.

"Here's what happened: The Church of Russia announced this week that it was breaking ties with the Ecumenical Patriarchate of Constantinople, which has primacy in Orthodoxy and which has decided to give autonomy to the Ukrainian Orthodox Church. This decision stems directly from Moscow's annexation of Crimea and its support for separatist rebels in eastern Ukraine, although Ukrainians had long been unhappy about their church remaining subordinate to Russia's, as it had been since 1686. This year, their president, Parliament and religious leaders petitioned the leader of the Constantinople Patriarchate, Bartholomew, to grant their church independence – or autocephaly, as it is known in the church," he said.

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These developments will have serious implications within Ukraine. Its mostly Orthodox population is divided among three main churches; the newly independent Ukrainian Orthodox Church of the Kyiv Patriarchate would gain influence and most likely seek to take over houses of worship and other property from the church under Moscow's jurisdiction, which, until now, was the largest in Ukraine and the only one recognized by other churches.

This will further strain relations between Ukraine and Russia. Also, the break in relations between Moscow and the Ecumenical Patriarchate could weaken the latter if other Orthodox churches follow Russia in rejecting Constantinople's primacy. The shock waves would affect relations between churches that find themselves on either side of the divide, forcing them, too, to sever ties. The churches of Poland, Serbia and Antioch (Syria) have already come out on Russia's side.

The Church of Greece could also be shaken, as a number of Greek clergymen may support Moscow against Bartholomew. Russian claims to leadership of the Orthodox Christians have appealed to many since Constantinople fell to the Ottoman Turks in 1453 and the patriarchs became subordinate to Muslim sultans. Furthermore, the Ecumenical Patriarchate's dialogue with other faiths, including the Roman Catholic Church, is deeply unpopular with hard-line Orthodox priests and monks.

Many monks in northern Greece's self-governing monastic community of Mount Athos – regarded as the jewel in the Ecumenical Patriarchate's crown – have pro-Russian tendencies. President Vladimir Putin has emphasized his nation's interest in Athos, and has visited it twice. One of Athos's 20 monasteries, Agios Panteleimon, is home to some 60 Ukrainian and Russian monks, with a Russian abbot.

There was no immediate response from Mount Athos following the break in ties between Moscow and Constantinople, but having to choose sides would be a problem for many monks. A representative of the Moscow church has said that Russian pilgrims to Mount Athos will not be able to receive communion there.

Greece and Russia, traditional friends, have already found themselves at odds on the political level, with Athens expelling Russian diplomats in July for trying to influence public opinion against an agreement with the Former Yugoslav Republic of Macedonia under which Greece's small neighbor would be renamed Northern Macedonia.

The Macedonian Orthodox Church, which broke away from the Church of Serbia in 1967 and is not in communion with any church, has appealed to Constantinople for independent status as the Archdiocese of Ohrid. The outcome of the appeal could depend on whether the agreement between Greece and Macedonia regarding the name is ratified by both countries. This, in turn, could complicate things further with Russia and other churches opposed to Ohrid's autonomy.

As in most schisms in Christianity's history, this one is determined as much by realpolitik and national interests as by dogma. Canonical issues can determine political behavior, while politics often dictate church developments. The Ecumenical Patriarchate is asserting its ancient right to grant autonomy to churches and to judge issues of church law. Constantinople was established by the Emperor Constantine in 330 and, as the "New Rome," it came just after Rome in seniority. The schism in 1054 left Constantinople the primary church in the East. It is these rights of primacy that the Ecumenical Patriarchate is determined to defend, despite its very reduced circumstances following the city's fall to the Ottomans and the withering of its own flock in Turkey, the author said.

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Russia wants to project its leadership of the Orthodox world as the "Third Rome," a role it took upon itself after breaking away from Constantinople in 1448, when its leadership disagreed with efforts to unite East and West Christendom. After 1453, many Orthodox, including the Greeks, looked to Russia for salvation from the Turks.

But today Ukraine is forging a separate identity after centuries of Russian domination, strengthening ties with the European Union and the United States. Ukraine's president, Petro Poroshenko, greeted the Ecumenical Patriarchate's announcement of its decision on Oct. 11 with fighting words.

"This is the collapse of Moscow's centuries-old claims for global domination as the Third Rome," he said. "The independence of our church is part of our pro-European and pro-Ukrainian policies that we have been consistently pursuing."

On Oct. 12, Russia's foreign minister, Sergei Lavrov, charged that the Ecumenical Patriarchate's decision was a "provocation" backed by the United States. On the same day, Mr. Putin discussed the issue at his Security Council. Patriarch Kirill, the leader of the Church of Russia, is a close ally of Mr. Putin's and has taken a hard line on Ukraine for years. On Monday, the governing body of the Russian Church, the Holy Synod, decided to break off relations with Constantinople.

Metropolitan Hilarion, head of the Russian church's external relations, stressed that Moscow would not abide by any decisions taken by the Ecumenical Patriarchate regarding the Ukrainian Church. "All these decisions are unlawful and canonically void," he said. "The Russian Orthodox Church does not recognize these decisions and will not follow them." He called on the Ecumenical Patriarchate to change its decision.

This is unlikely, as Bartholomew has long seen the Russian church as trying to undermine his authority. Patriarch Kirill stayed away from a Holy and Great Council hosted by Bartholomew on Crete in 2016, a meeting of all Orthodox church leaders aimed at promoting unity, which had been 55 years in the making. The patriarchs of Bulgaria, Georgia and Antioch also did not attend.

Turkey, which has enjoyed good ties lately with both Russia and Ukraine, has stayed out of the issue so far.

As for the United States, it has stressed its support for both Ukraine and Bartholomew. "The United States respects the ability of Ukraine's Orthodox religious leaders and followers to pursue autocephaly according to their beliefs," said a State Department spokeswoman, Heather Nauert, in September. "We respect the ecumenical patriarch as a voice of religious tolerance and interfaith dialogue."

Bartholomew needs American support. He is considered the spiritual head of the world's Orthodox Christians and "first among equals" of the 14 church leaders. Also, the Greek Orthodox Archdiocese of America falls under Constantinople's direct jurisdiction.

Losing the Church of Russia, and any that might follow its lead, would be a serious blow to the Ecumenical Patriarchate. In church time, 1721 is not so long ago – that's when Peter the Great abolished the Russian patriarchate, appointing a Holy Synod instead. Nor is 1918, when several decades of persecution of Russian, Ukrainian and other Christians began.

The feeling at the Patriarchate, in a run-down part of Istanbul, is that things must be done correctly and when the time is right. In nearly 2,000 years, the Church of Constantinople has seen several empires rise and fall, but has remained standing – chiefly by defending its historical role and responsibility, despite the temporal cost.