The capture of Mosul by Isis means a radical change in the political geography of Iraq and Syria. Moreover, the impact of this event will soon be felt across the Middle East as governments take on board the fact that a Sunni proto-caliphate is spreading across northern Iraq and Syria.
The next few weeks will be crucial in determining the outcome of Isis's startling success in taking over a city of 1.4 million people, garrisoned by a large Iraqi security force, with as few as 1,300 fighters. Will victory in Mosul be followed by success in other provinces where there is a heavy concentration of Sunni, such as Salahuddin, Anbar and Diyala? Already, the insurgents have captured the important oil refinery town of Baiji with scarcely a shot fired by simply calling ahead by phone to tell the police and army to lay down their weapons and withdraw.
These spectacular advances by Isis would not be happening unless there was tacit support and no armed resistance from the Sunni Arab community in northern and central Iraq. Many people rightly suspect and fear Isis's bloodthirsty and sectarian fanaticism, but for the moment these suspicions and fears have been pushed to one side by even greater hatred of Iraq's Shia-dominated government.
This may not last: Iraqi government officials speak of a counterattack led by special "anti-terrorist" forces that are better trained, motivated and armed than the bulk of the Iraqi army. It may be that the Kurds will use their peshmerga troops in Nineveh and Kirkuk provinces to drive back Isis and create facts on the ground in areas often rich in oil, in Kirkuk and Nineveh provinces. A successful counter-offensive could happen but the failure of the Iraqi army to retake Fallujah, a much smaller city than Mosul, in the six months since it fell in January does not bode well for the government. If the Isis advance takes more towns and villages, then the territory lost to the government may become too large to reconquer.
But Isis too has its weaknesses: in the past it has isolated itself by its fierce determination to monopolise power, impose fundamentalist Islamic norms and persecute or kill all who differ from it. This enabled the Americans to turn many Sunni against it in 2006 and 2007. So far reports from Mosul suggest it is being much more circumspect, telling government employees to turn up for work and not harassing the population, though this may not last. People in Mosul are wondering who they fear most: Isis or the government. Anger against the latter will grow if it resorts to indiscriminate bombing and shelling of Mosul as it has done in Fallujah.
Followers of Isis have flooded Twitter with pictures of the bodies of their enemies but they have also used the medium to show functioning hospitals and a consultative administrative process. It is not clear which will prevail in Iraq: possibly both.
The fall of Mosul has changed the balance of power between Iraq's three main communities; Shia, Sunni and Kurds. Shia rule in non-Shia areas has received a blow from which it will be difficult for it to recover; Kurdish dominance in mixed Kurdish-Arab areas will expand; the five or six million Sunni Arabs will never be marginalised again.
It is not just in Iraq that the balance of power is changing. The Iraq-Syrian border no longer exists for most practical purposes. In Syria Isis forces will become vastly more powerful because the movement can draw on fighters, weapons and money from its newly conquered territories in Iraq. The rest of the Syrian military opposition to President Bashar al-Assad will find it difficult to compete on the battlefield with Isis if it manages to consolidate its recent victories.
