Operation Inherent Resolve

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. 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. 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. 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. 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. 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 ==