Operation Inherent Resolve (OIR) is the United States military's operational name for the international war against the Islamic State (IS) including both a campaign in Iraq and a campaign in Syria, with a closely related campaign in Libya.
Through 18 September 2018, the U.S. Army's III Armored Corps was responsible for Combined Joint Task Force – Operation Inherent Resolve (CJTF—OIR) and were replaced by the XVIII Airborne Corps. The campaign was primarily waged by American and British forces in support of local allies, most prominently the Iraqi Security Forces (ISF) and Syrian Democratic Forces (SDF). Combat ground troops, mostly special forces, infantry, and artillery have also been deployed, especially in Iraq. Of the airstrikes, some 80% have been conducted by the military of the United States, with the rest by the United Kingdom (Operation Shader), Australia, Belgium, Canada, Denmark, France, Jordan, the Netherlands, Saudi Arabia, Turkey, and the United Arab Emirates.
By October 2017, around the time of IS's territorial defeat in Iraq, CJTF—OIR claimed that around 80,000 IS militants had been killed by it and its allies (excluding those targeted by Russian and Syrian air strikes). According to the Pentagon, by March 2019, the day of IS's territorial defeat in Syria, CJTF—OIR and its partner forces had liberated nearly 110,000 square kilometers (42,471 square miles) of land and 7.7 million people from IS, the vast majority of the self-proclaimed caliphate's territory and subjects. By the end of August 2019, it had conducted 34,573 strikes. Tens of thousands more were killed by partner forces on the ground (the SDF alone claimed to have killed 25,336 IS fighters by the end of 2017). According to Airwars, between 8,220 and 13,299 civilians were killed in the airstrikes in Syria and Iraq, with an additional 1,437 civilians killed in other operations.
Background
The United States relied on a combination of legal frameworks to justify its use of force against ISIS in Iraq and Syria, namely: military assistance on request, self-defence under Article 51 of the United Nations (UN) Charter, and the "unwilling or unable" doctrine. However, this legal reasoning was not unanimously accepted by other coalition members, resulting in differing geographic scopes of operation—some states restricted their involvement to Iraq, while others also conducted operations in Syria. Moreover, these justifications continue to be the subject of legal debate among scholars.
Legal basis under international law
International law prohibits the use of force against another state, as provided in Article 2(4) of the UN Charter. However, there are two exceptions to 'violate' this legal prohibition, which is through authorisation of the United Nations Security Council (UNSC), as stated in Article 42 of the UN Charter, and in self-defence, in accordance with Article 51 of the UN Charter.
Military assistance on request
Military assistance provided at the request of a state does not require UN authorisation nor the invocation of Article 51, as it falls within a state's sovereign right under customary international law to request such assistance and does not necessarily entail the use of force. As such, it does not constitute a 'violation' of the prohibition on the use of force. However, in order to remain within the legal framework of military assistance—rather than constituting an intervention that breaches the prohibition on the use of force—the inviting state determines the scale and scope of the intervening force, as the operation's sole purpose is to provide assistance to the inviting sovereignty. Furthermore, the inviting state cannot legally authorise the use of force on foreign territory, as this would violate Article 2(4) of the UN Charter, therefore, military assistance on request is confined to the borders of the inviting state.
In 2014, the Iraqi government submitted two formal letters to the UNSC, requesting military assistance in response to the ongoing threat posed by ISIS along its borders. Several states participating in OIR acted solely on the basis of this request, thereby limiting their operations to Iraqi territory, as the Iraqi government had no legal authority to authorise military action on Syrian soil. By responding exclusively to Iraq's request, the scale and scope of the foreign military presence was determined through agreements with the Iraqi authorities and remained confined within Iraq's borders, despite ISIS maintaining a stronghold in eastern Syria. The Obama administration relied on this legal framework—military assistance upon request—to justify its operations within Iraq. However, as Syrian President Bashar al-Assad had not granted consent for foreign military intervention, an alternative legal basis was required to justify military action against ISIS in Syria.
Additionally, scholars such as Ashley Deeks have argued that the U.S. tends to avoid relying on military assistance upon request as a legal framework, as such operations are entirely dependent on the level of consent granted by the inviting state and could require the U.S. to withdraw its forces should that state revoke its request.
Article 51: Individual or Collective Self-defence
To justify its operations within Syria, the United States invoked Article 51 of the UN Charter, citing the principle of collective self-defence on behalf of Iraq. This was based on the Iraqi government's request for a U.S.-led international campaign against ISIS. Simultaneously, the United States also invoked the right of individual self-defence, referencing the threat posed by ISIS to its own national security.
Article 51 of the UN Charter recognizes the "inherent right of individual or collective self-defence if an armed attack occurs against a Member of the United Nations". In 1986, during the Nicaraqua v. United States case, the International Court of Justice (ICJ) spelled out several pre-conditions for the lawful invocation of Article 51:
- A state may only invoke individual self-defence if it has been the victim of an 'armed attack';
- Collective self-defence requires a victim state to declare itself as such and to formally request collective measures from other states;
- Any invocation of Article 51 must be reported to the UNSC.
In its letters to the UN Security Council, the Iraqi government formally requested military assistance in response to an armed attack against its sovereignty. Moreover, given that ISIS-controlled territory extended across a significant area spanning both Iraq and Syria, the Iraqi government argued that, in order to neutralise the threat posed by ISIS to Iraq, it was necessary to eradicate the group entirely—including through military operations on Syrian territory under ISIS control. Based on this request, in which Iraq declared itself a 'victim' of an armed attack, the Obama administration announced the invocation of collective self-defence on Iraq's behalf against ISIS, via a letter submitted to the Security Council. By doing so, the necessary conditions for a lawful invocation of Article 51 were met.
However, according to the ICJ, extraterritorial self-defensive operations against a non-state actor within the territory of a host state require the consent of that state's government, unless the conduct of the non-state actor can be legally attributed to it. This condition was not fulfilled in the case of Syria, as President Assad was actively engaged in fighting ISIS and, moreover, had neither granted consent to the U.S. nor received any formal request to permit military operations on Syrian soil. Consequently, despite invoking Article 51, the Obama administration continued to face legal challenges in justifying its military actions against ISIS in Syria.
Unwilling or unable doctrine
To address these legal challenges and justify its operations against ISIS in Syria, the United States, in its letter to the UNSC, also invoked the "unwilling or unable" doctrine. It accused the Syrian regime of both an inability and unwillingness to prevent ISIS from using Syrian territory to launch attacks against Iraq. According to the 'unwilling or unable' doctrine, a state has a responsibility to eliminate threats originating from within its borders. If it is deemed 'unable'—for instance, due to insufficient military capability—or 'unwilling', due to a lack of political will or action, the international community may assume the responsibility of neutralising the threat posed by non-state actors operating within the hosting state's territory.
However, although the 'unwilling or unable' doctrine was invoked by several states participating in OIR to justify their involvement, it remains without clear legal standing under international law. Moreover, some scholars have questioned the applicability of the term 'unwilling', noting that the Assad regime was actively engaged in combat against ISIS. Despite public expressions of willingness by the Syrian government to cooperate in efforts to defeat ISIS, the U.S. maintained that, due to the Assad regime's failure to eliminate ISIS within Syrian territory, it was not obligated to seek permission for conducting military operations on Syrian soil.
Despite these questions concerning its validity, the Obama administration used the 'unwilling or unable' doctrine to justify the military intervention against ISIS in Syria. By doing so, this doctrine became an extension of the invocation of self-defence by the U.S., to make self-defensive action in Syria justified as response to the armed attacks perpetrated by ISIS performed from Syrian soil.
History
2014
Unlike their coalition partners, and unlike previous combat operations, no name was initially given to the conflict against IS by the U.S. government. The decision to keep the conflict nameless drew considerable media criticism.
The U.S. decided in October 2014 to name its military efforts against IS as "Operation Inherent Resolve"; the U.S. Central Command (CENTCOM) news release announcing the name noted that:
According to CENTCOM officials, the name INHERENT RESOLVE is intended to reflect the unwavering resolve and deep commitment of the U.S. and partner nations in the region and around the globe to eliminate the terrorist group ISIL and the threat they pose to Iraq, the region and the wider international community. It also symbolizes the willingness and dedication of coalition members to work closely with our friends in the region and apply all available dimensions of national power necessary—diplomatic, informational, military, economic—to degrade and ultimately destroy ISIL.
The US Defense Department announced at the end of October 2014 that troops operating in support of Operation Inherent Resolve after 15 June were eligible for the Global War on Terrorism Expeditionary Medal.
By 4 December 2014, three U.S. service members had died from accidents or non-combat injuries.
2015
In November 2015, Commodore Captain Augustus Bennett commanding the USS Kearsarge (LHD-3) Amphibious Ready Group entered the 5th Fleet AOR in conjunction with the 26th Marine Expeditionary Unit under the command of Colonel Robert Fulford, consisting of the, USS Arlington (LPD-24) and USS Oak Hill (LSD-51) to commence airstrikes on IS. Prior to this, the ARG rendezvoused with the Turkish Navy for Egemen 2015. They concluded their OIR mission on 10 March with a total of 130 sorties and 60 strikes.
On 22 October 2015, a U.S. Master Sergeant, Joshua Wheeler, was killed in action when he, with about 30 other U.S. special operations soldiers and a Peshmerga unit, conducted a prison break near Hawija in the disputed territories of Northern Iraq, in which about 70 hostages were rescued, five IS members were captured and "a number" were killed or wounded. Sergeant First Class Thomas Payne was awarded the Medal of Honor for his actions during the operation. The Kurdistan Regional Government said after the raid that none of the 15 prisoners it was intended to rescue were found.
From May, North American Rockwell OV-10 Broncos joined the operation, flying more than 120 combat sorties over 82 days. It is speculated they provided close air support for special forces missions. The experiment ended satisfactorily, but a US Air Force spokesman stated it remains unlikely they will invest in reactivating the OV-10 on a regular basis because of the overhead cost of operating an additional aircraft type.
2016
By 9 March 2016, nearly 11,000 airstrikes had been launched on IS (and occasionally Al-Nusra), killing over 27,000 fighters and striking over 22,000 targets, including 139 tanks, 371 Humvees, and 1,216 pieces of oil infrastructure. Approximately 80% of these airstrikes have been conducted by American forces, with the remaining 20% being launched by other members of the coalition, such as the United Kingdom and Australia. A total of 7,268 strikes hit targets in Iraq, while 3,602 hit targets in Syria. On 12 June 2016, it was reported that 120 IS leaders, commanders, propagandists, recruiters and other high-value individuals were killed so far this year.
Until March 2016, U.S. military members were ineligible for Campaign Medals and other service decorations due to the continuing ambiguous nature of the continuing U.S. involvement in Iraq. However, on 30 March 2016, U.S. Secretary of Defense Ash Carter announced the creation of a new medal, named "Inherent Resolve Campaign Medal".
On 3 June 2016, aircraft flying from the USS Harry S. Truman in the Mediterranean Sea began airstrikes on IS. On 16 June 2016, AV-8B II+ Harriers of the 13th MEU flying from the USS Boxer in the Persian Gulf also began airstrikes on IS, marking the first time the U.S. Navy used ship-based aircraft from both the Mediterranean and the Persian Gulf at the same time during Operation Inherent Resolve.