The recent gains in northern Iraq by the jihadist Islamic State of Iraq and the Levant (Isis), an offshoot of al-Qaeda, are worrying and have shocked the international community. The spectre of renewed sectarian violence, even the possibility of all-out civil war has once again resurfaced in Iraq.

Isis has taken control of the northern cities of Mosul, Iraq’s second largest city with a population of over two million, and Tikrit, Saddam Hussein’s hometown, both in the Sunni heartland, and is battling for control of other cities.

Isis’ first important victory was last January when, fuelled by war in Syria – where it already controls large areas of territory – it took control of the city of Fallujah, in what was a major propaganda coup for the jihadist group. This should have served as a wake-up call to both the Iraqi government and the international community, but unfortunately it did not.

The fact that Mosul fell without a fight is a major concern; most of the 30,000 Iraqi troops fled as a force of just 800 to 1,000 Isis fighters advanced. This shows that segments of the Iraqi army, which is supposedly American trained, either lacks proper leadership or is heavily demoralised, or both.

The savagery of Isis was also immediately evident: draconian Islamic regulations were imposed on the cities they captured and the Iraqi soldiers who stayed behind were brutally massacred, and their executions posted on the internet. In Mosul, furthermore, Isis captured a lot of Iraqi army equipment, mostly US-donated, looted the banks of millions of dollars and freed about 1,000 prisoners, most of whom joined their ranks.

There are estimated to be about 10,000 Isis fighters in Iraq and Syria, including foreigners (of whom about 400 are radical British Muslims), and these have been joined by other Sunni militant groups, including Saddam Hussein-era officers and soldiers, and disaffected Sunni tribal fighters.

Unfortunately, Isis has managed to exploit the disillusionment felt by many Sunni Arabs towards the Shi’ite-led government of Prime Minister Nouri Maliki, who has done little to govern in the interests of all Iraqis and who last year began a purge of Sunni leaders. Maliki’s failure to share the nation’s oil wealth, allegations of corruption in government circles, as well as discrimination against Sunnis in key appointments in the security forces have all contributed towards Sunni anger and paved the way for Isis to exploit this situation.

How serious is the situation in Iraq and is it likely to become a failed state? Can the international community help prevent the country from breaking up and is there a military or political solution to this crisis, or both?

First of all, the worst case scenario is that Isis will continue to make gains in some Sunni areas; they are unlikely to take Baghdad or cities in the southern Shi’ite region or the northern Kurdish province. The Shi’ites are already mobilising against Isis after a plea from their spiritual leader, Grand Ayatollah Ali al-Sistani, while the Kurds are fighting and repelling advances by the jihadists.

Isis control of Sunni territory is nevertheless very worrying and needs to the reversed; otherwise Iraq will be a de facto partitioned state. Besides being bad news for Iraq, this situation also presents a direct threat to the world as Isis-controlled territory will be used as a base to launch a global jihad.

How far can Isis advance in Iraq? To put things in perspective, while Isis seems to have plenty of money, it has no air power and no heavy weapons and is obviously outnumbered by the Iraqi army. It does not enjoy unanimous support among Sunnis and the more it tries to make advances, the more its resources will be stretched. Furthermore, Iraq is not Syria, and with the right type of military and political strategy, this jihadist insurgency can be defeated.

However, this war cannot be won by military means alone. The Iraqi government needs to regain the trust of the Sunni population, especially the tribal leaders; the first step towards this goal would be the establishment of a national unity government consisting of Shi’ites, Sunnis and Kurds. Real concessions will have to be made to the Sunnis and Kurds, and the time has come for Prime Minister Maliki to consider stepping down. It is clear that the Americans, who have been officially asked by Maliki to consider airstrikes against Isis, are losing patience with the Iraqi Prime Minister.

On Tuesday, former secretary of state Hillary Clinton said that Maliki “has failed as a leader”, while a number of lawmakers from both parties said that Maliki had to go if Iraq had any chance of forming a national unity government. Republican Senator John McCain, for example, said in an interview about Maliki: “He’s got to step down. There’s no reconciliation with him and the Sunnis. He should form a coalition government and leave”.

Iran has the potential to play a constructive role

Although the Americans have a moral duty to help Iraq – the US-led invasion and the catastrophic mistakes committed in the aftermath of Saddam Hussein’s overthrow laid the basis for today’s crisis – Washington’s options are limited. There is no chance of sending American troops in a combat role, but the US can help with more humanitarian aid, intelligence sharing, counter-insurgency advice and even possibly limited air strikes to stem the advances of Isis.

US President Barack Obama has already announced that 300 military advisers are to be sent to Iraq, and this is certainly welcome.

At the same time, however, Washington needs to demand major concessions from Baghdad in return for its support, most notably the creation of a national unity government consisting of Sunnis, Shi’ites and Kurds.

This crisis has also presented an opportunity for Obama to improve relations with Iran, Maliki’s powerful Shi’ite ally. Iran, which ironically is probably the most stable country in the region, will not tolerate an Iraq overrun by Sunnis jihadists, and like Washington, has an interest in a stable and united Iraq. Teheran has the potential to play a very constructive role in Iraq – not by direct military intervention, which will probably aggravate Sunni-Shi’ite tensions – but by exerting pressure on Maliki to be a more inclusive leader.

The US should take advantage of this situation to engage diplomatically with Iran, just as it had done over Teheran’s nuclear programme. Britain’s announcement last week that it is to re-open its embassy in Iran is certainly a welcome step; has the time arrived for Washington to do the same?

A genuine rapprochement between the US and Iran, where both sides would have to eat humble pie, has the potential to bring about positive change in the entire region, and could be an encouraging sign in an otherwise very depressing situation.

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