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.

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