SLAVERY divided not only the United States, but also its churches. The Methodists, Presbyterians, Baptists and others all split North from South, and some did not reunite for more than 100 years. Others, like the Southern Baptist Convention, never did.

Now some of these same churches are facing a rift over homosexuality that is proving more intractable than any social issue since slavery. It is not an explosion, but a slow burn that has been smoldering in some denominations for about 30 years — longer than the battle over women’s ordination.

Women won those battles in mainline Protestant churches, and though the churches bled some members, they stayed largely intact. But it is far from clear whether the strife over homosexuality will end the same way. That is why all eyes are now on the Episcopal Church. With 2.3 million members, it is only the 15th-largest in the United States, but it is a venerable, wealthy institution that has produced one out of four United States presidents, the Washington National Cathedral — and a civil war over homosexuality that has brought it closer to schism than any other church. Last week, Episcopalians were handed an ultimatum by the top leaders in the Anglican Communion: stop authorizing blessings of gay couples and ordaining gay bishops — or face banishment from the Communion. They were given until Sept. 30 to decide.

The Presbyterians, Lutherans and Methodists have also had battles over homosexuality, but the conflict in the Episcopalian Church is magnified because it is playing out on an international stage. The Episcopal Church is a member of the Anglican Communion, a global affiliation of 38 member churches that grew out of the Church of England. The Communion claims a membership of 77 million — making it the world’s third-largest church body after the Roman Catholic and Orthodox Churches.