THE assault to push Islamic State (Isis) out of its Mosul stronghold in Iraq is a pivotal moment in the war against the extremists.

Isis occupied Mosul two years ago as its fighters swarmed across Iraq in a seemingly unstoppable blitzkrieg.

Since then, Isis has turned the beleaguered city into its seat of power – a potent symbol which encouraged thousands of volunteers, many of them from Europe, to answer the group’s jihadist war cry.

But now Isis is in retreat. It has been pushed back from the outskirts of Baghdad and its fighters face overwhelming odds in the fight to hang on to Mosul.

What is most heartening about this rapid reversal in fortunes is the role played by the Iraqi army. The Isis fighters haven’t been routed by well-equipped Western ground forces – the heavy lifting has been done by Iraqi and Kurdish Peshmerga soldiers fighting to liberate their country.

Two years ago, the Iraqi Army collapsed in the face of Isis fanatics; today they are ready to take back their country.

The West does have a role to play, however.

It must do everything it can to help the thousands of civilians trapped as Mosul burns.

Diplomats must put pressure on the attacking forces to set up safe corridors so people can get out.

Sadly, the creation of safe zones needs agreement on both sides – and Isis never plays by the normal rules of combat.

We may have seen the high watermark of Isis’s territorial gains but no one can be sure what will come next.

Will it withdraw and fight an insurgency in Iraq? Or will it send scores of Western fighters back home to Europe and the UK so they can exact a terrible revenge?

Now is not the time for the West to drop its guard.