Reluctant US returns to Iraq frontline amid humanitarian crisis
President Obama has authorised air strikes but says he will not send US troops back to Iraq
The United States has been reluctant to get drawn back into Iraq in military terms and for good reason.
For one thing, President Barack Obama came to office seeking to extricate the US from foreign wars, not to begin new ones.
He remains convinced that Iraq's problems are fundamentally political.
The Obama administration wants to see the back of Iraq's Prime Minister Nouri Maliki, whom it sees as ruling in a narrow, partisan way, in favour of his own Shia Arab majority.
Corrupt and cronyism has sapped the morale and effectiveness of the Iraqi military.
ReconnaissanceWashington has also been reluctant to arm the Kurdish Peshmerga forces for fear of accelerating the trend towards Kurdish independence - a move that would have widespread ramifications within the region.
Hundreds of thousands of people have been displaced by the fighting in the north of Iraq
However, the gains made by jihadist militants from the Islamic State (IS) - what used to be called Isis - has focused minds in Washington.
A few weeks ago, when IS-led forces were advancing on the Iraqi capital, Baghdad, the US reinforced the protection of its embassy and also deployed manned and unmanned aircraft.
For more than a month now the US has been flying some 50 sorties a day to build up a detailed intelligence picture of what is happening on the ground.
It has also established links into key Iraqi security headquarters so that this information can be processed and used if necessary.
But despite completing this initial assessment no action was forthcoming.
Mr Obama seemed to be dragging his feet with more and more US commentators urging him to act.
Air dropsIn the event, it was not events on the road to Baghdad that prompted US action but a crisis further north on the borders of the autonomous Kurdish areas.
During its advance on Baghdad, IS fighters have plundered a significant quantity of heavy equipment and ammunition from the government's forces.
The US has begun making humanitarian air drops in the Sinjar area
Units have simply melted away leaving behind their equipment. Bases have been overrun.
This has given the Islamic State a significant advantage over the Peshmerga, who have been forced to pull-back in a number of areas.
It was the plight of religious minorities fleeing the IS advance that compelled Mr Obama to act.
The initial step has been to drop water and supplies to thousands of refugees taking refuge in the hills above Sinjar, a town in northern Iraq, using one C-17 and two C-130 transporters, escorted by two F/A-18 fighters.
But US Defence Secretary Chuck Hagel also made it clear that targeted air strikes were also a distinct possibility.
Within hours two US warplanes struck what a US spokesman described as an Islamic State mobile artillery piece that was shelling Kurdish forces on the approaches to Irbil. This though is in many ways a statement of intent.
One air strike is not going to turn the Islamic State tide. But the jihadists can be in no doubt that despite all the prevarication the Americans now mean business.
ConditionsThe US has considerable air power within striking distance in the region.
It could stage aircraft out of bases in Kuwait; potentially even Turkey (though it is not clear if the government in Ankara would allow such action); and it has the aircraft carrier, the USS George H W Bush in the Persian Gulf, as did the two jets that hit the artillery piece.
The F/A-18 fighters that escorted the air drop probably came from the carrier, as did the two jets that hit the artillery piece.
Mr Hagel set out two reasons for potential air strikes - firstly the local humanitarian situation around Sinjar, and secondly to protect American personnel should they approach Irbil, the capital of Iraq's Kurdistan Region, where the US maintains a consulate.
The defence secretary emphasised that an enduring response to the IS threat would require greater political reconciliation and a strengthening of the Iraqi military.
US personnel would provide more assistance, he noted, "once Iraq has formed a new government".
Regional instabilitySo to this extent support for the central government in Baghdad is still conditional.
The US has been reluctant to arm the Kurdish Peshmerga forces
Rapid intervention in the north was a special case merited by the unfolding humanitarian catastrophe, but how much more support might the Americans give to the Kurds?
Amid all the talk of centrifugal forces in Iraq, the Kurdish north has the greatest degree of autonomy - some would argue it is already half-way out of the door of the Iraqi state.
Such a move would have huge implications for Turkey, Syria and Iran who all have Kurdish minorities.
The Kurdish fighters may well be most in need of US support, but whether this goes beyond air power to weaponry, ammunition, logistical support and so on is uncertain.
There are certainly voices in Washington urging that much more should be done.
Indeed there is also a renewal of the debate about the nature of the Iraqi state itself.
Is the current arrangement sustainable? Is it already on the way to breaking down? And what might replace it?
Given the wider instability in the region - the chaos in Syria; the Gaza crisis; problems in Lebanon, Yemen and elsewhere, the Middle East is facing perhaps the greatest level of instability in more than a generation.
In retrospect, what was hailed as the "Arab Spring" now looks like a misleading moment of hope; a prelude to a dark and bitter future.
Rise of Islamic State
'Mortars crashing around us'
Angry Iraqi PM in show of force
No baby boom
Ebola dilemma
Fine romance
Uptalk rising
Cowboy country
Click