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The most surprising element of the fight appears to have been the Iraqi forces' failure - despite extensive regional and international support - to expel the hybrid insurgent group from the country.

On the defensive against the Combined Joint Task Force, IS has managed to withstand over 11,573 airstrikes on its positions (as of 13 April) and still retains roughly .

Is this down to IS' fighting prowess, or have political factors undermined the tactical advantage Iraqi forces have had? 

IS' strategy is dynamic and opportunistic, " in response to new opportunities". Their asymmetric strategy advocates decentralisation, especially when battlefield losses require alternative victories - in the eyes of their fighters, the group must always appear to be making progress, regardless of reality.

The tendency for reliance on decentralised attacks and the opening of new theatres to distract from lost battles is predictable, and allows for a better understanding of their vulnerabilities. Although " flexibility to undertake their own operations, senior leadership detrimentally lacks any oversight on the battlefield".

IS' strategy promotes purposeful destabilisation, such as through their destruction of religious, cultural and administrative sites when in retreat

IS' aggressive offensive approach  of the many junior commanders who hold very considerable influence in the execution of operations. This has been "chronic tactical restlessness," an approach which "can help sustain morale and extend the surviving troops' operational experience, but exhausts their manpower and continually erodes their overall force strength," proving very costly in the long run.

Iraqi paramilitaries advance towards the ancient city of Hatra during an offensive to retake the area from IS [AFP]

IS' strategy promotes , such as through their destruction of religious, cultural, and administrative sites when in retreat. Rather than killin off the enemy in a single blow, it weakends its immune system so that little diseases can become life threatening.

As a result of years of turbulence, Iraq has almost no immune system left. IS' survival relies on regional unrest - and their strength capitalizes on the ease with which a region can be destabilised through sectarian tensions and civilian casualties, compared with the difficulty of reconstruction.

The latter is a scenario coalition forces have unintentionally assisted in through recent airstrikes. However, Lt. Gen. Stephen Townsend  "the March 17 airstrike in Jidada wouldn't have collapsed the building on its own". Numerous sources confirm the building was likely filled with human shields, acting as bait for the strikes, to benefit IS propaganda. Such tactics perpetuate instability, wherein the true power of their strategy lies.

IS leadership under Baghdadi endured significant losses during the  that saw Sunni tribal participation. Since then, purges of Sunni government positions and " brutalizing Sunni [tribesmen] in their homes in the guise of rooting out terrorism," sparked protests throughout Anbar Province.

IS used these protests as a cover for recruitment, providing militias with manpower and thereby gaining the support of Sunni tribes who had ousted Zarqawi's men a decade earlier.

However, one obstacle for IS in reorienting its strategy in Iraq back towards an insurgency, will come from its territory's residents, as a future insurgency would rely on.

Until then, IS' main challenge as it continues losing territory is to sustain itself as an organisation ", and its universal caliphate claims become increasingly outlandish."

, a retired U.S. Army Special Forces Colonel following the military situation in Iraq, explains their major limitation: While functioning more as a regular army than merely an insurgency or terrorist group, and by fighting force with force (something most insurgencies do not do), IS still lacks the types of access benefitting other nation states (in terms of trade, assistance, and access to modern equipment from other nations).

Maliki gutted the leadership of ISF, filling it with sycophants loyal to him

The ISF should have been able to defeat IS easily, given its strategic advantage as a regular army, fighting in open warfare against a non-state, former insurgency-turned military actor, whose decentralised operations cannot be coordinated or controlled. Due to political factors however, this has not been the case.

While Iraq has long suffered from sectarian tensions between its majority Shia and minority Sunni population, Witty argues IS was especially aided by the policies of [former] PM Maliki which alienated much of Iraq's Sunni population. 

Although making up roughly 30 percent of the population, Sunnis were a powerful minority under Saddam Hussein, yet littleto make them feel as though they are full partners in a national project. The US did little to curb Maliki's disenfranchisement of Sunnis, even less so after their 2011 withdrawal. 

Maliki gutted the leadership of ISF, filling it with sycophants loyal to him versus selecting leaders based upon their military abilities and talents. 

	Displaced Iraqis leave their homes near Hatra, captured by IS in a lightning 2014 offensive [AFP]

This in turn led to the degrading of the ISF, who were unable to prevent IS from using the civil war to establish a power base. ISF consequently took far longer to shape into a formidable force, and once Mosul is liberated, it will have the difficult task of convincing the Iraqi Sunni population there that they are not the same deserters who fled Mosul.

Tactically the ISF's greatest weakness has been insufficient manpower, causing that have given IS great mobility. The ISF need  to reduce the lethality of IS delaying tactics, in order to consolidate recaptured areas.

Until now, coalition forces have been slow to dispense necessary manpower, which has in turn limited clearing plans and slowed progress. It has also to expand their sphere of influence, helping the PMUs who in 2014, prevented the militants from reaching Baghdad.

Since then, their presence has been crucial to the offensive. Regrettably, as Boghani , their violence against Sunnis "has already alienated some of the country's Sunni population." 

Prime Minister Abadi has been struggling, however, to contain these militias and prevent them from becoming a new Iraqi revolutionary guard loyal to Tehran. Due to the militias' long record of sectarian abuses, their ongoing presence "could one day result in another Sunni insurgence - like the one that led to IS' rise."

Kurdish aspirations for independence have made negotiating the handover of territory seized from IS particularly complicated.

The seizure involved looting of Sunni Arab homes and has reignited historic political divisions in Northern Iraq between Kurds and Sunnis.

Tackling the country's political issues must also be part of the endgame

As the Institute for the Study of War , over-reliance on the Kurdish forces, "risks encouraging ethnic conflict due to the relative empowerment of the Kurds at the expense of Sunni Arab local powerbrokers" which the ISF and coalition partners from successfully destroying IS.

Because the Iraqi Kurdish political parties have expressed no interest in returning Sinjar to Baghdad, after numerous failed attempts to exert federal control over the region.

As the Kurds continue to disregard the authority of Baghdad, and as the Iraqi government is unable to maintain neutrality, US mediation is crucial if future stabilisation is to be a real possibility.

The Mosul offensive began on an "" because of the Obama administration's rushed offensive ahead of the 2016 presidential election, prompting a series of decisive strategic mistakes.

ISF and Kurdish forces were insufficiently prepared at the time, slowing efforts significantly. Failing to surround Mosul and cut off IS' supply route from Syria - it could be argued - were the most pivotal blunder of the operation. In hindsight, the coalition forces could have been more operationally effective had they taken the time to rectify logistical oversights. All of this might have prevented the need for permanent US long-term troop deployment.

Until Abadi's visit, it was unclear how committed the Trump Administration would be to the coalition effort. Officials have since clarified the financial and operational commitment the US has in store.

Abadi must use this opportunity to guarantee the reconstruction effort is successful, by ensuring his coalition partners are committed to Iraqi long-term stability.

Tackling the country's political issues must also be part of the endgame, as both are crucial to ensuring stabilisation. Promises of troop deployment however do not yet clearly signal such a comprehensive strategy exists beyond the military one.

Sarah Schneider is a final year undergraduate at the University of Exeter pursuing a degree in Arabic, Middle Eastern Studies, and International Relations. She specializes in geopolitical developments in the Middle East, contemporary armed Islamist movements, and security risk analysis.

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Opinions expressed in this article remain those of the author and do not necessarily represent those of °®Âþµº, its editorial board or staff.