As the well-trained, black-uniformed forces of the Islamic State of Iraq and the Levant sweep across north and central Iraq, the entire Middle East shudders.
In less time than it took U.S.-led forces to reach Baghdad in 2003, this jihadist group has taken control of almost a third of Iraq, the country with the fourth-largest oil reserves in the world.
As a result of its two-day blitzkrieg, ISIL is perched atop a major export pipeline in Mosul, has surrounded Iraq's largest refinery in Baiji, has conquered Tikrit, the centre of Saddam Hussein's Sunni empire, is on the edge of capturing one of the Shia world's most sacred sites in Samarra, has shamed the once-mighty Iraqi military and sits on the doorstep to Baghdad.
Iraq's security forces seem powerless to stop them.
Prime Minister Nouri al-Maliki has appealed to retreating troops to rally at a point northwest of Baghdad, from which they will battle the "outsiders."
Foreign Minister Hoshyar Zebari, a member of the Kurdish community, said Baghdad and the autonomous Kurdish government must work together "to flush out these foreign fighters."
And Muqtada al-Sadr, a powerful Shia cleric, called for the creation of special militia units to safeguard religious sites.
In Washington, the Obama administration said it "will provide additional assistance to the Iraqi government to combat the threat from [ISIL]," while Shia Iran said it will help Iraq combat "terrorism."
"All this could have been averted if the United States had been able to keep 10 [thousand] to 15,000 troops in the country," said Bill Roggio, editor of the Long War Journal. "They would have provided the intel, the logistical support and the equipment to combat a threat like this."
"Instead, we're watching as everything the U.S. built to prop up the Iraqi government is collapsing," said Mr. Roggio, a U.S. Army veteran and senior fellow at the Washington-based Foundation for Defence of Democracies."
Even the line of defence Mr. al-Maliki has chosen as a rally point – the town of Taji – is well short of what has been the line of defence in the past.
Mr. al-Maliki "has effectively ceded northern Iraq" to the enemy, said Jessica Lewis, research director of the Institute for the Study of War in Washington. This includes yielding Samarra – site of the al-Askari Mosque, a historic Shia shrine.
Fierce fighting broke out Wednesday at the entrance to the city.
It is to be expected that ISIL wants to capture the place. The group, which began in Iraq as the Islamic State of Iraq, then expanded to Syria as ISIL with considerable success against the regime of Bashar al-Assad, has returned to Iraq to fulfill its initial aims.
The group's leader, Abu Bakr al-Baghdadi, is from Samarra, and the group is strongly opposed to what it considers to be Shia apostasy.
The speed and success of ISIL's assaults this week suggest a sophisticated operation.
"They have very good intel, logistical experience, supply routes, weapons and lots of manpower," said Mr. Roggio. Probably tens of thousands of fighters, he estimates.
"All that means there's a lot of money behind them," he added.
The source of those funds is unknown for now but Alastair Crooke, a former British intelligence operative and author of Resistance: The Essence of the Islamist Revolution, is willing to wager Saudi money is behind it.
Mr. Crooke argues Salafist jihadists, backed by Saudis, have adopted a sectarian discourse to demonize the Shiites and cement the Sunni identity. "They see it as a way to unite the Sunni nation," he said.
In Iraq, he says, "a great deal of the Sunni hostility to the Shiites comes from a strong sense of grievance because the newly empowered Shia government has taken Sunni power and position and wealth."
As well, since Mr. al-Assad seems entrenched in Damascus (thanks to backing from Iran) his primary jihadist opponent, ISIL, may be trying to take the fight to Iran by luring it into battle in Iraq.
"Should Iran actually enter this conflict – sending in the Revolutionary Guard, for example – there'll be a real civil war in Iraq," said Mr. Roggio, who emphasized that such a move would bring all the Sunnis together in opposition.
Iraqi forces on their own, however, appear unable to repel the ISIL militants.
For five months, they couldn't get them out of areas of Anbar province, including Fallujah, where they set up a mini-state.
"It will require a combination of [Kurdish] Peshmerga and Iraqi security forces, with a lot of U.S. help," said Mr. Roggio, referring to U.S. contributions of intelligence, logistics, weapons and air support.
As for Iran's offer to help, "it would best be deployed in support of the Shia region in the South," he said; not getting into fights in the Sunni heartland, where ISIL has been so successful.
In a remarkably short time, ISIL has achieved a major goal – establishing an Islamic "state" within Iraq. It has Mosul as its capital and Syria as its training ground.
"It may get pushed back a bit," said Mr. Roggio, "it may have overreached. But it looks like it'll stay in place for some time to come."