"IDLIB Province is the largest al Qaeda safe haven since 9/11," said Brett McGurk, special presidential envoy for the Global Coalition to Counter Isis.

So you wouldn't think that the United States would object to the Syrian government reconquering it — especially since US forces in Syria have no way of reaching Idlib, in the country's northwestern corner, and neither do America's Kurdish allies.

But you might be wrong about the US stance, because the Syrian regime's troops attacking Idlib would have Russian bombers helping them. Turkey might also object, as President Recep Tayyib Erdogan was surreptitiously helping the al Qaeda rebels in Syria earlier in the war and has already posted Turkish troops at "observation posts" inside Idlib Province to protect the status quo.

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We're going to find out which way Turkey and the US jump quite soon, because Idlib is next on the list.

Over the past two years, Bashar al-Assad's Syrian regime has recaptured first the rebel-held part of Aleppo, Syria's biggest city, then the eastern outskirts of Damascus, the capital, and most recently the areas down south near Israel and Jordan where the rebellion began. Idlib is next.

It has to be Idlib because that's where all the jihadi fighters who surrendered after those other defeats were sent.

The influx of Islamist fighters and their families has virtually doubled the province's population to two million in the past two years. Assad will want to finish the job while the Russian air force is still in Syria, so the offensive will probably start next month.

It will require intense bombing, as the Syrian army is short of ground troops, and there are bound to be anguished international protests about civilian casualties in the crowded province. That would provide an excuse for either Washington or Ankara to intervene and stop the attack if they want, but do they?

Erdogan would have to pull the Turkish troops out of Idlib if he wants to avoid a clash with the Syrian army, which would be rather embarrassing, and he hates to be embarrassed.

He is already having to eat a good deal of humble pie in the financial crisis that is crippling the Turkish economy at home, and this would be a second helping.

On the other hand, Erdogan has already had to change his line once and accept that Assad will survive as Syria's dictator. That makes it kind of hard for him to argue now that Syria cannot be allowed to take Idlib back, especially since the real power in Idlib is Hayyat Tahrir al-Sham, the many-times-renamed Syrian branch of al Qaeda.

Logically, Erdogan should not be getting involved in a foreign war when he is already in a shouting match with Donald Trump and the Turkish economy is in a nose-dive. But he is erratic, emotional and over-confident, so he might just dig his heels in.

As for Trump's own decision on Idlib, national interest decrees that he should just sit back and let it happen. What's not to love about an event that destroys al Qaeda's only territorial base in the Middle East at no cost in American money or lives?

But if Trump doesn't intervene, America's hard right will complain he is allowing a further expansion of Russian power in the Middle East, while his Israeli allies will protest again at the use of "Iranian troops" (really mostly Iraqi, Afghan and Syrian mercenaries paid by Iran) in the battle.

And Trump, too, is erratic, emotional and over-confident.

If the Idlib operation goes off without a major hitch involving Turkish or American military intervention, it will be the last major battle of the Syrian civil war.

There would remain the task of persuading Turkish and American troops to leave the country, but that should not involve fighting.

There is a deal that could work. The Turkish and US armies both pull out of Syria, and the Syrian army replaces them to ensure there is no comeback by Islamic State and no base there for Kurdish separatists seeking to break away from Turkey.

The Syrian Kurds are rewarded with limited self-government including control over education, language and local spending. And the Russians go home too, since Assad no longer needs their help.

That would be the sensible thing to do ... but this is the Middle East, so nobody knows what will happen.

Gwynne Dyer's new book is "Growing Pains: The Future of Democracy (and Work)"