Since the incursion of ISIS into western and northern Iraq, groups normally at odds are forming ad hoc coalitions to repel the jihadist army.

Following the U.S. airstrikes on August 8 to defend Yazidis trapped on Sinjar Mountain, members of the Syrian Kurdish People’s Protection Units (YPG) joined forces with the Kurdish Workers Party (PKK) to form the self-defense units. Together, they managed to defeat ISIS while the Kurdish fighters regrouped and rearmed, such as at the battle of Makhmour near the Kurdish capital of Erbil.

The United States considers the PKK to be a terrorist organization given its decades-long struggle with NATO ally Turkey.

Likewise, members of Shi’ite militias from the Peace Brigades and Hezbollah Battalions joined forces with Kurdish pesh merga fighters and the Iraqi Army -- using military Humvees provided by the U.S. -- to liberate the Turkmen city of Amerli on August 31, which had suffered a siege from ISIS lasting nearly 80 days.

The military operation was

reportedly coordinated on the ground by Qassem Suleimani, the Iranian operator who has served as a political power broker in Iraq and has managed terrorist operations across the globe. The Peace Brigades are tied to cleric Muqtada al-Sadr, whose Shi’ite militia had battled the U.S. during the Iraq War, and the Hezbollah Battalions have alleged ties to Iran’s al-Quds force, which is led by Mr. Suleimani.

An uncanny alliance was also formed among Kurdish pesh merga fighters, the Iraqi Army, and local Sunni tribes near Kirkuk -- the largely Kurdish city whose legal fate has been a cause of political friction between Erbil and Baghdad. Nevertheless, in cooperation with Sunni groups opposed to ISIS, such as the Naqshbandi Army, the pesh merga managed to prevent ISIS from capturing the city.

While the president of Iraqi Kurdistan, Masoud Barzani, and politicians in Baghdad have squabbled over how Kirkuk's fate will be decided (either through a referendum per Article 140 of the constitution or through facts on the ground), both parties have agreed to table this and other related issues regarding territorial sovereignty and oil and gas revenues until the ISIS threat has been settled.

A catalyst for such cases of inter-sectarian cooperation has been the formation of a new government under the leadership of Prime Minister Haider al-Abadi, who has stressed the need for national unification following the sectarian governance of Nouri al-Maliki.

For instance, al-Abadi has criticized the use of the quota system to fill key cabinet and administrative positions within the government and has pressed for appointments to be based on competence and expertise rather than sectarian allegiances. In a press conference, al-Abadi also announced the importance of bringing private militias under the control of the Iraqi Army as a way to allay the fears of Sunnis who have been targeted by Shi’ite forces.

While Sunnis and Shi’ites have cooperated, such as in the joint effort between Sunni tribes and the Iraqi Army to reclaim the Haditha Dam located in the Sunni-dominated Anbar province, some Sunni communities are still skeptical of the army given its recent history of religious persecution.

For instance, residents of Mosul, which is currently held by ISIS, are wary of what might follow a liberation of the city by the Iraqi Army or Shi’ite militias. However, according to Atheel al-Nujaifi, the governor of Nineveh province, negotiations are underway to assemble a force of Sunni groups and tribesmen from Anbar, Diyala, and Salahuddin provinces to assist the U.S., the Iraqi Army, and the pesh merga in the battle to recapture Mosul.

Many Sunnis have turned against ISIS as the basis for their allegiance and their shared antipathy toward al-Maliki has proven to be tenuous and fragile following ISIS's brutality against Sunni locals and the creation of a new, more inclusive government in Baghdad.

Although together these various forces -- Kurdish, Sunni, Shia, and those from the Iraqi Army -- have succeeded in collectively reclaiming some territory, it is likely that foreign intervention, such as the last-minute rescue effort to stop the massacre at Mount Sinjar, will be required to eliminate the ISIS threat all together.

According to Maj. Gen. Fadel Barwari, the U.S.-trained head of the Iraqi Special Operations Forces, Iraqi forces are able to reclaim towns and cities like Tikrit temporarily and force ISIS to engage in “tactical withdrawal.” However, once the insurgents regroup, they then harass and attack government forces from all angles, making it difficult to hold on to territory.

“The inability of Iraqi forces to control the liberated land comes from the lack of traditional defense mechanisms such as air forces, logistical abilities to build fortifications, and the necessary supplies to link battlefronts,” Barwari

told Al-Monitor.

Defeating ISIS in the long-term will thus likely require more outside intervention from countries with greater capabilities, and the U.S. has led a global diplomatic effort to build an international coalition committed to dismantling the organization.

At a NATO summit in Wales, President Obama encouraged fellow NATO allies to develop a strategy to defeat ISIS. Turkey expressed reluctance in joining the effort -- motivated, in part, by its animus toward the PKK -- but the Arab League, while thus far withholding specific details, has pledged to help stop ISIS.

A looming question is whether or how to take the fight to ISIS in Syria, where it has planted the capital of its proclaimed caliphate in the city of Raqqa.

In Syria, ISIS has continued its fight against President Bashar al-Assad, and it is looking to isolate and strangle the remnants of the rebel opposition. In Aleppo, for instance, ISIS is threatening to take hold of the countryside north of the city and cut off supply lines linking the rebels to Turkey, which has long been aiding the rebels.

In his speech on September 10, President Obama announced his desire to support the Syrian rebels who are battling both jihadist groups like ISIS and the Syrian regime as part of a multifaceted strategy that also involves airstrikes, military advice and assistance to Iraq, and stemming the flow of foreign fighters, money, propaganda to "degrade and ultimately destroy" ISIS.