The forces that would like to destroy the organization cannot, and those that could do not wish to The Islamic State this week executed kidnapped American journalist Steven Sotloff, in “retaliation” for US bombing of its area of control in Iraq – once more indicating the group’s savage brutality.But while Islamic State may be almost without rival in terms of its capacity for cruelty, events on the ground in Iraq and to a lesser extent in Syria are indicating its limitations as a military force. Tactical setbacks, however, have not yet cast a serious shadow over the future existence of Islamic State.In early August, the terror movement reached far into Iraq in a lightning offensive that left it 45 km.from the Kurdish capital of Arbil and in possession of the city of Mosul and the Mosul dam, which provides water and electricity to northern Iraq and its capital. The group’s fighters humiliated the Iraqi army in the taking of Mosul, and the Kurdish Peshmerga forces in the capture of the Sinjar mountain area.Islamic State went on to carry out atrocities against the Yazidi population of the Sinjar area and the Christians of the Mosul area, creating a large refugee population. It was only air strikes by the US Air Force commencing on August 8 which prevented the fall of Arbil.Islamic State remains deployed close to the Kurdish capital. This reporter last week visited one of the front-line positions of the Kurdish Peshmerga, at Khazer northwest of Arbil. The lines around the city are eerily quiet at the moment.This is because Islamic State knows that were it to attempt to roll across the bare, flat ground towards the city, the US air response would be swift and fierce, and would result in the obliteration of the jihadi force.The halting of the jihadi advance toward Arbil is testimony to the might of US arms, when directed with will and a clear goal.The US has also been engaged – in cooperation with the Peshmerga, Shi’ite militias and the Iraqi army – in beginning to turn back Islamic State advances in western Iraq.This week, the siege on the city of Amerli was lifted by Iraqi and Shi’ite militia forces, paving the way for the reconquest of Salahuddin province. The advance was preceded by US air strikes on Islamic State positions in the town.The Peshmerga has also had a good few days. The strategic Mosul dam was recaptured in late August, in a joint operation with Iraqi forces; this week, the town of Zumar was retaken.Evidence is emerging that US Special Operations Forces are also engaged in the Iraq battles. It is not clear what precise role these forces are playing, but their presence has no doubt contributed to the relatively strong showing of the Iraqi and Kurdish forces in recent days.The evidence indicates that the Islamic State tactics which enabled it to achieve rapid gains in Iraq in the course of the summer are of less application when defending areas against a determined attacker.Islamic State has fast-moving, mobile light infantry forces and employs terror tactics to intimidate populations.But it has limited manpower and no particularly original tactical abilities in defense, beyond its fighters’ willingness for self-sacrifice.Further west in Syria, when Islamic State fighters have faced the well-motivated and determined Kurdish YPG militia, they have failed to gain ground.In Hasakeh province and further west in the beleaguered Kobani enclave, the lightly armed but highly motivated and well-trained YPG fighters have succeeded in holding off the jihadis (albeit with heavy losses on the Kurdish side).This was so even when Islamic State began to deploy US weapons systems captured in Mosul against the Kurds in Kobani; the enclave remains intact.So Islamic State is not invulnerable. Nevertheless, its continued existence is under no immediate threat, because of strategic – not tactical – issues.Yet the forces that would like to destroy Islamic State cannot, and those that could do not wish to.Air strikes can be useful in enabling Iraqi forces and the Peshmerga to eat away at the eastern edges of Islamic State territory in Iraq. But air power alone cannot root out the jihadis from their heartlands in Syria or indeed, from their Iraqi conquests as a whole. This could only be achieved by ground forces.Syrian President Bashar Assad’s army would certainly like to reunite eastern Syria with the rest of the country.But Assad’s forces have been losing ground to Islamic State in Raqqa province – the latest defeat being the loss of the Tabqa air base, and the subsequent massacre of the garrison.The Iraqi army and its allied Shi’ite militias would also like to win back the areas lost to Islamic State, but there is no reason to believe these forces have the offensive capacity to do so. The Iranians are likely in the process of seeking to transform these forces, in a similar way to that achieved with regard to Assad’s fighters in late 2012/early 2013.Again, the Iraqi Shi’ite are relevant only with regard to Iraq; the Islamic State heartland remains in Syria.The US lacks a clear strategy for how to deal with Islamic State other than placing clear red lines before Arbil and Baghdad, and assisting the Iraqi army and the Kurds. And Syria remains largely off-limits, it would appear, despite the increasingly fictional nature of the border between Iraq and the country to its west.There is no political will for the kind of commitment of Western forces that could obliterate Islamic State. And Kurdish forces – both YPG and the Peshmerga – are interested in defending and maintaining Kurdish areas of control, not in offensive operations.This means that despite the setbacks it has been suffering over the previous week, the survival of Islamic State does not appear to be in question at the moment. Islamic State will exist until someone has the ability and the will to destroy it – and this time does not appear to be imminent.