Almost the whole burden of preserving the Anglican Communion from schism now rests on the shoulders of the Episcopal Church in the United States. It has about seven months to decide whether to comply with a tough package of conditions drawn up by the Anglican primates in Tanzania this week. If they fail, the Archbishop of Canterbury, Dr Rowan Williams, will refuse to invite their bishops to the next Lambeth Conference in 2008, membership of which defines a bishop as being in the Anglican Communion. Because of his power to exclude, the drawing up of the invitee list is one of the rare occasions when the Archbishop of Canterbury functions as an Anglican Pope.

For Dr Williams the Tanzania outcome is light at the end of a long, dark tunnel. Prior to the meeting, one widely expected outcome was that the two factions in the Anglican Communion would, under his presidency, split it down the middle (or across the Equator, given how much the split is geographical as well as theological). The older, white, Western churches would continue their slow progress towards liberalising their discipline, particularly towards homosexuality, while the newer, black churches would continue to go their own more fundamentalist way. But now, instead of a bad-tempered break into two roughly equal halves, the more likely outcome is a split 35 against one. And it would be the odd one out which chose that fate for itself.

It may well do so. Provincial autonomy - the right of each branch of Anglicanism to decide its own policy - is more an article of faith in American Anglicanism than anywhere else for historical reasons: 1776 was an ecclesiastical as well as a political breaking point. Similarly, there is a tendency for Episcopalians to see themselves as trendsetters regarding such issues as homosexuality, as they were over women's ordination. So the climbdown required is a hard one. But the future direction of the Anglican Communion now seems set, with proposals for an "Anglican Covenant" which will permanently constrain provincial autonomy for the sake of wider Anglican unity and prevent this crisis from repeating itself every few years. The Americans may not want to pay that price, and prefer isolation. It would be a messy break-up, because a minority of Episcopalian bishops will want to stay with the larger Anglican family.

It has not always been easy for Anglicanism's ecumenical partners, especially the Roman Catholic Church, to see what holds Anglicanism together. For a while the links were historical, cultural and linguistic. The Lambeth Conference, which brought every Anglican bishop into the company of his brethren once a decade for two weeks, provided also a bond of personal affection and fellowship. But all these unifying factors have needed fair weather to work: they look fragile in a storm. The Anglican Covenant, which will no doubt incorporate theological insights from the work of the Anglican-Roman Catholic International Commission, will give Anglicanism for the first time an official ecclesiology, a coherent account of itself as a world body. Given the strains that the bonds of friendship have been under - some archbishops even refused to join the others for a photograph at the end of their Tanzania meeting - this more formal structure of unity could yet save Anglicanism from itself.