The immediate reason is that the Islamic State's atrocities against enemies and civilians are so appalling that the world cannot sit back and watch. There are also concerns that IS can reach across the world to supporters here in Australia, as recent arrests in Sydney and Melbourne indicate.

On a deeper level, Islamic State, also known as ISIL, threatens the stability of the region if it inflames Sunni extremism in countries such as Saudi Arabia and exacerbates sectarian tensions in Shiite power Iran.

Might Australia be drawn back into a lengthy war in the Middle East?

Yes. Most experts believe the overall coalition campaign will be a long one, possibly lasting years. Some, including US defence chief General Martin Dempsey, have openly flagged the possibility that a deeper involvement, even combat troops, may be needed if the current strategy is not successful.

What is the strategy – and is it the right one?

The general view of the experts is that the combination of coalition air strikes and ground fighting by Iraqi and Kurdish forces – bolstered by advice and training by the US, Australia, probably Britain and Arab states in the region – is the best strategy in a difficult situation.

But it has flaws. Much of the Iraqi Army is not up to the job. Training them will take time.

Meanwhile in Syria, the US and several Arab nations are conducting air strikes, with plans to train and help moderate rebels in the civil war as ground troops against IS. But even more than in Iraq, these ground troop allies are not strong enough to hold large amounts of territory.

What will victory look like?

The stated objective is to "degrade and destroy" Islamic State. While it hopefully can be degraded to the point that it is no longer such a danger, it won't be destroyed altogether. The best hope is a stable Iraq that can maintain its own sovereignty. There is no viable strategy at the moment to remake Syria, leaving the question: if IS is degraded, what then? Likely a vacuum is created that will be filled either by the brutal Assad regime or by extremists groups such as Jabhat al-Nusra that are rivals to IS.

Is there a risk of mission creep?

Mission creep is a commonly used term but is not quite right for this situation. The mission, to degrade and destroy IS, is unlikely to change. A better term is "strategy and tactics creep", which may happen, drawing Australia further into the war if the present approach doesn't work.

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