Islamic extremists have seized control of Fallujah, Mosul, Iraq's second city, and Tikrit with what seems bewildering speed. Now, emboldened, they are talking of marching on Baghdad. The United States' belief of a "sovereign, stable and self-reliant" Iraq, enunciated less than three years ago by President Barack Obama when the last American troops left the country, lies in tatters.
Yet neither the success of the Islamic State of Iraq and al-Sham forces nor the swiftness of their advance should come as big surprises. The seeds for such a development were sown as soon as Saddam Hussein was toppled.
The creation of a stable and thriving Iraq was always going to depend on the country's ethnic and religious groups being persuaded that compromise and consensus was in their interests. Much of that, in turn, relied on the new Iraqi administration being able to demonstrate that it could govern strongly and effectively. While the Americans were propping up that government, limited progress was made. However, a virtual civil war in 2006-7 between the Shiites, who comprise 60 per cent of the population, and the Sunnis, who have ruled Iraq for most of the past century, re-emphasised the inherent potential for conflict.
With the withdrawal of the US forces, it soon became clear that neither of the prerequisites for a stable Iraq was being met. Prime Minister Nouri al-Maliki has been a failure.
In parliamentary elections in April, his Shiite-dominated political bloc failed to gain a majority, prompting paralysis. The degree of his impotence was demonstrated last week when he could not assemble a quorum to ask parliament to declare a state of emergency. His administration is riddled with corruption and, most damagingly, has ruled increasingly in the interests of the Shiites.
This has effectively ruled out the opportunity for reconciliation. Disaffected Sunnis have come to see armed confrontation as their only means of reclaiming any degree of power.
This has laid the foundation for the takeover of much of the Sunni heartland by Isis, an al-Qaeda splinter group. The Iraqi army has scarcely put a fight, hobbled by the desertion of Sunni officers and men and a panic engendered by the brutality of the Isis forces. But if Isis is now just an hour's drive from Baghdad, that does not indicate the fall of the city is imminent or even likely.
The Iraqi capital lies in Shiite territory, and Isis will face much stiffer resistance, not least thanks to the intervention of Iran, a fellow Shiite state. This may come either directly or through the strengthening of Shiite militias.
This reinforcement does not mean, however, that the Iraqi Government will easily be able to reclaim the territory lost to Isis. Nor will the Kurds readily relinquish the northern oil city of Kirkuk, which they have long claimed as their capital. Probably the likeliest scenario, as has been the case since the demise of Saddam Hussein, is that Iraq, always an artificial construct, will break up along ethnic and sectarian lines. Most worryingly, this would see a radical Sunni state extending across Iraq and areas of Syria already seized by Isis.
The group's imposition of a strict version of Sharia law in Mosul suggests obvious comparisons with the Taleban in Afghanistan and the potential for that state to become a breeding ground for terrorism.
This has alarmed the US sufficiently for President Obama to state that no options have been ruled out. But there will be no appetite for further embroilment in Iraq. That reinforces the likelihood of a break-up. Only the emergence of a strongman able to unite the country in the manner achieved by Saddam Hussein may stand in the way of this.