FOREIGN governments insist that diplomacy is the only answer to the war in Syria. Yet on November 5th Lakhdar Brahimi, a respected UN envoy, postponed a peace conference in Geneva planned for the end of this month. It was just the latest delay, despite years of effort.

Failure presents Western leaders with a brutal choice. Among their many aims in Syria, three stand out: a negotiated settlement to end the violence; a desire to rein in Iran’s efforts to exert influence in the region; and a commitment to remove Bashar Assad, Syria’s president, from power. The bitter lesson from Mr Brahimi is that, at this time, the West can secure either the first aim or the other two, but not all three together.

To see why, consider the lessons of other civil wars, which we assess in this week’s briefing. Syria is bogged down in endless killing. Early in the uprising, Western support might have ousted Mr Assad and preserved Syria’s sectarian harmony. That was what this newspaper at first recommended, but the West—and Barack Obama in particular—held back. Now, after more than 110,000 people have died during 30 months of violence, it is too late. Not only have many rebels fallen under the spell of Sunni fanaticism, but history suggests that, unless civil wars end in victory after 12 months or so, they tend to drag on for years. Like many civil-war leaders Mr Assad may prefer to prolong the fighting rather than risk compromise. The rebels, too, will battle on in the knowledge that surrender is likely to mean death.

Hence the argument for a negotiated settlement that might bring forward an end to the fighting and spare Syrian lives. The effort is worth it—about 40% of civil wars end through negotiation. But the odds on success are already long. It makes no sense to insist on conditions that would make the talks still more likely to fail.

That is why Iran is central. It is the country most actively pumping money into Mr Assad’s war machine, fuelling the combat. Often the only way to shorten a conflict like Syria’s is for sponsoring countries to cut off funds and arms to their proxies and to offer the services of a large UN peacekeeping force to provide security for both sides. Mr Assad’s backers in Iran and Russia, and the rebels’ in Saudi Arabia and Qatar, could create a “mutually hurting stalemate” by blocking access to the finances or weaponry for both sides until they agree to make up, as happened in Kosovo in 1999.

No sponsor will stop unilaterally—that would be tantamount to accepting defeat. But peace can follow when outsiders act in concert, as happened in 1990 at the end of the civil war in neighbouring Lebanon. Securing a co-ordinated withdrawal of support is Syria’s best hope. But this requires Iran and Saudi Arabia, fierce regional rivals, to come together around a table, which, at the very least, means admitting Iran as a full partner to the diplomacy.

If Iran has to be involved, so does Mr Assad. Western leaders have said that he must agree to leave power as a precondition for negotiations, but when they had the chance to oust him, they didn’t. If Mr Assad is shut out of Syria as an entry ticket to the talks, neither he nor Iran will be interested in turning up. Even if he gets to the table, Mr Assad would need pushing by Iran and Russia to accept a power-sharing deal. That is why the price of peace may now be to allow Mr Assad and Iran a stake in a future Syria—at least for the time being.

These are two bitter pills. Mr Assad has committed terrible crimes and Iran’s succour for his regime has been an outrage. But the price of yet more bluster from Mr Obama, of pretending that the West can get everything it wants right now, will be more lost Syrian lives.