The capture of Iraqi cities Mosul and Tikrit by al Qaeda-influenced jihadis has not only redrawn the map of a country corroded by sectarian hatred.
It could also redesign Middle Eastern national boundaries set nearly a century ago after the fall of the Ottoman empire, and lead to a forging of new regional alliances.
As well-armed forces of the Islamic State of Iraq and the Levant (ISIL) raised their black flags over Mosul this week, routing an Iraqi army that fled rather than fight, the future of Iraq as a unitary state hung in the balance.
As they pressed south towards Baghdad, the rest of the region, the United States and other powers woke up to the prospect that this Jihadi comeback could establish a dangerous base in the heart of the Middle East - an Afghanistan on the Mediterranean.
"What we are witnessing is the fragmentation of power. The government of Prime Minister Nuri al-Maliki will never be able to centralize power in the same way he has," says Fawaz Gerges, a Middle East expert at the London School of Economics.
"We are seeing a redrawing of boundaries for sure," he said.
As the conflict escalated, Iraq's most senior Shi'ite cleric on Friday urged his followers to take up arms to defend themselves against the Sunni revolt. A rare message from Grand Ayatollah Ali al-Sistani, the highest religious authority for Shi'ites in Iraq, said people should unite to fight back against the insurgency by ISIL fighters and former Saddam loyalists.
Sistanis's intervention followed the failure of the government of Nuri al-Maliki, the Shi'ite prime minister re-elected in April, to convene a quorum in parliament to grant him emergency powers. Sunni and Kurdish lawmakers had stayed away.
A Stunned Region
The peshmerga forces of the Kurdish region of northern Iraq meanwhile seized Kirkuk, the oil-rich region bordering their self-governing territory, stepping into a security vacuum to claim a prize they have always regarded as their own.
The ease with which ISIL, a Sunni Jihadi movement that has fed on the civil war in Syria and staked out the ungoverned space between eastern Syria and western Iraq, swept into Iraqi cities has stunned a region seemingly inured to shock.
The insurgents, led by Iraqis who broke with al-Qaeda, are pressing south to Baghdad.
Some experts say they may be over-reaching. But while ISIL's predecessors were defeated in 2007-08 by Sunni tribal militias empowered by U.S. forces, ISIL has exploited Sunni anger at Maliki's sectarianism and inherited networks from Saddam Hussein's army.
"ISIL has been able to embed itself with a disaffected and alienated Sunni community", says Gerges.
"In fact, the most important development about ISIL in the last year is its ability to recruit former officers and soldiers of the dissolved Iraqi army. If you observe how ISIL has been waging war you see a skilled mini army, confident, that has command and control, is motivated and using war tactics."
The ISIL advance has been joined by former Baathist officers who were loyal to Saddam as well as disaffected armed groups and tribes who want to topple Maliki. So far the towns and cities that have fallen to the militants have been Sunni.
"The Sunnis of Iraq are willing to go to bed with the devil to defeat Maliki, this is where the danger lies," Gerges said.
Redrawing The Borders
The million-strong Iraqi army, by contrast, trained by the United States at a cost of more than $20bn, is hobbled by low morale and corruption that impedes its supply lines.
Its effectiveness is hurt by a perception among Sunnis that it pursues the hostile interests of the Shi'ites, a majority in Iraq, raised to power by the U.S. led invasion of 2003.
The Kurdish capture of Kirkuk overturns a fragile balance of power that has held Iraq together since Saddam's fall.
Iraq's Kurds have done well since 2003, running their own affairs while being given a fixed percentage of the country's overall oil revenue. But with full control of Kirkuk - and the vast oil deposits beneath it - they could earn more on their own, eliminating the incentive to remain part of a failing Iraq.
U.S. President Barack Obama threatened military strikes against ISIL, highlighting the gravity of the group's threat to redraw borders in a region already wracked by war.
Hayder al-Khoei, Associate Fellow at Chatham House, said the jihadi onslaught leaves Washington in an awkward position.
"With US-made military vehicles and weapons being paraded by jihadists in Mosul, policy-makers will be questioning the effectiveness of providing Baghdad with even more military hardware that may end up in the hands of the very people they want to defeat," he said.
Ambivalent To Hostile
Reactions inside the region are ambivalent to hostile.
Deep down Saudi Arabia and its Sunni allies, which have never reconciled themselves to the loss of Sunni-ruled Iraq to the Shi'ites, detest Maliki for his alliance with non-Arab Shi'ite Iran. They would like to see Maliki brought down but did not want al-Qaeda affiliates to be the ones doing it.
They believe Iran, backed by its allies, wants to build a Shi'ite crescent from Iraq through Syria to Lebanon.
"I can imagine a Saudi official saying 'the wrong people are doing the right thing'," said Jamal Khashoggi, head of a TV news station owned by Saudi billionaire Prince Alwaleed bin Talal.
On the other hand, Iran, which has strong leverage in Iraq, is so alarmed by the ISIL advances that it may be ready to cooperate with Washington in helping Baghdad fight back.
A senior Iranian official told Reuters the idea is being discussed among the Islamic Republic's leadership. For now, officials say, Iran will send its neighbour advisers and weaponry, although probably not troops, to help Maliki.
Turkey, which has turned a blind eye to Jihadis crossing its border to fight Syrian President Bashar al-Assad, is not ready to intervene militarily because it fears its own sectarian demons and will focus on securing its borders, experts say.
The Kurds, crucial players, will likely resist Baghdad's calls to be drawn in by sending troops to recapture Mosul and other towns. They will instead consolidate their presence in Kirkuk and along their borders, Kurdish officials said.
Iran Weighing In
Iraq watchers say ISIL, estimated to have a few thousand fighters inside Iraq, won't be able to advance into Baghdad, a capital of 6 million where Maliki has his special forces deployed, backed by Iranian-trained militias.
"I don't think they will run as far as Baghdad. They haven't got the numbers, they overreached themselves...It is more about the weakness of the Iraqi state than it is about the state of ISIL," said Toby Dodge, Director of the Middle East Centre at the London School of Economics.
Just as there is little chance of ISIL taking over the Shi'ite-dominated capital, the Iraqi army is unlikely to dislodge ISIL from Mosul or regain full control of the north of the country, even with Shi'ite militia volunteers and likely Iranian support.
With the rising Sunni insurgency, Iran may have to weigh in to salvage its ally and Tehran's influence in Iraq as it did in neighbouring Syria.
Diplomatic sources said Iran already has high-ranking commanders, including two close aides of Qassem Suleimani, the commander of the Revolutionary Guards elite Quds force, regularly holding meetings with Maliki.
Malikis' mobilisation of Shi'ite militias, endorsed by the highest religious authority, has the potential to trigger all-out sectarian strife, analysts say.
And there are concerns that Iraq might disintegrate into sectarian and tribal conflict, shattering into Shi'ite, Sunni and Kurdish entities.
"Maliki is playing with fire by trying to unleash Shi'ite militias, this is a recipe for disaster. That's exactly what ISIL wants - to trigger all-out sectarian war," Gerges said.
"Iraq has never healed, it is a mutilated country. The crisis is reaching a tipping point whereby Iraq will splinter into 3 or 4 states or reconcile. To reconcile you need a new leader, a new mindset and you don't have it there."