The Iraqi government's battle to control Falluja
The predictions for Iraq are dire. Analysts both inside and outside the country warn Iraq is once more poised on the brink of a sectarian civil war.
In Anbar province, the country's largest and most restive, troops from the Shia-dominated government in Baghdad have been sent to regain control of the mostly Sunni cities of Falluja and Ramadi from al-Qaeda and other insurgents.
The Americans have offered Baghdad support, in the form of surveillance drones, helicopters and Hellfire missiles, and so has Iran's military.
This raises the bizarre possibility of the US and Iran both backing the same side in an increasingly complex standoff.
But what will it take for Baghdad to wrest back control?
How did the Americans succeed last time in 2006/7?
And crucially, what does it mean for the region if Baghdad fails and effectively loses an entire province?
Hotbed of insurgency
This is as much a socio-political problem for Baghdad as a military one.
There will be no permanent solution to be found in simply deploying brute force or better intelligence.
Anbar province has long been a hotbed of Sunni insurgency. It is where US forces suffered about a third of their casualties during their eight-year occupation.
In the years following the US-led invasion of 2003, al-Qaeda came close to establishing a mini-state in Anbar province.
It took the US Marine Corps some of the bloodiest and most intense fighting since the Vietnam War to retake the city of Falluja in 2004, leaving much of it in ruins.
But in 2006 a coalition of US, British and Iraqi forces persuaded Anbar's Sunni tribes to expel al-Qaeda.
How did they do this?
US and British generals, including America's General David Petraeus, orchestrated a temporary "surge" of thousands of extra troops into Anbar.
But this was only the visible part of their strategy.
It was preceded by a discreet, behind-the-scenes campaign, together with their Iraqi partners and backed by cash, to convince the Sunni tribal chiefs that their future lay with the government rather than with the insurgents.
Their words fell on fertile ground.
Local Iraqi residents, who had initially welcomed al-Qaeda's resistance to the US occupation, were chafing at the draconian rules imposed on them by extremists.
In some places even smoking cigarettes was punishable by having fingers chopped off, and one chieftain complained that al-Qaeda had brought them nothing but severed heads in bread baskets.
The result was the "Sahwa" - the Sunni tribal awakening that drove out al-Qaeda and established a modicum of security in Anbar.
But since then the situation has regressed badly.
The Shia-dominated government of Prime Minister Nouri Maliki has failed to deliver on the promises made to Anbar's Sunnis.
They feel, with some justification, marginalised and discriminated against, shut out of key roles in government, harassed, arrested and brutalised.
In short, it was an opportunity squandered to bring the Sunni tribes into the mainstream machinery of government.
Muwaffaq Al-Rubaie, Iraq's former national security adviser, recently told the BBC:
"Al-Qaeda are coming back because the measures we have put in place to include the Sunni community into the federal government have been dismantled".
So given this deep-rooted resentment by Anbar's Sunni tribes against their government in Baghdad, however much hardware is deployed against the insurgents, it is unlikely to deliver a lasting peace.
At stake in all this is not just the future integrity and security of Iraq, but that of the whole region.
For al-Qaeda's local franchise, the Islamic State in Iraq and the Levant (ISIS), the situation is akin to a perfect storm.
Across the common border in Syria, its forces are thriving on the chaos of a three-year old civil war, drawing in jihadist recruits from all over the Middle East and Europe.
The border, that runs through an intensely tribal area, is mostly porous, allowing a constant flow of arms and men in both directions.
Al-Qaeda's members in Iraq, having been largely defeated in Anbar six years ago, have since been able to regroup and rearm.
They have also been able to exploit the genuine grievances of the Sunni tribes there, facilitating their takeover of police stations, armouries and even driving round in police vehicles.
If the Baghdad government is unable to pacify Anbar's main towns of Falluja and Ramadi then it will have lost control of a huge territorial area.
Given that the Kurdish north already has virtual autonomy this could hasten a future disintegration of Iraq.
But the problem extends well beyond Iraq's borders.
With Syria wracked by a conflict now spilling over its border with Lebanon, and the whole region witnessing a proxy struggle between the interests of Shia Iran and Sunni Saudi Arabia, the prospect of another large, ungoverned space where al-Qaeda is able to train, recruit and plan is deeply worrying to Washington and its Gulf Arab allies.
Hence this week's announcement of an expedited order of 100 Hellfire missiles and several ScanEagle surveillance drones to bolster the Baghdad government's efforts.
This could go one of several ways. The Baghdad government, all too aware of what a tough nut Falluja will be to crack, could just decide to sit this out.
With its forces encircling the city and many of the families already having fled to safer parts, the government will be hoping to persuade the Sunni tribes to evict al-Qaeda, sparing everyone from bloodshed.
If this fails, then it may decide it has no choice but to go in, backed by tanks and artillery, resulting in a bloodbath that will hardly endear the government to the local inhabitants.
With Washington making it clear there will be no US boots on the ground in support, there is also no guarantee that an all-out military assault would succeed.
But the bigger problem is longer-term and political. The only way Falluja, Ramadi and the whole province of Anbar will become stable and settled is for Baghdad to deliver good governance.
For that to happen, a completely new approach will be needed.
"It will be difficult for the Maliki government", says Brig Ben Barrie of London-based think tank International Institute of Strategic Studies, "to solve the problem of Sunnis supporting al-Qaeda because since Iraq took control of its own security [in 2011] his disenfranchisement of Sunnis has meant they have effectively been treated as an enemy".