I argue that the UN Charter allows the use of force against non-state actors if their attacks meet the ‘armed attack’ threshold and the host state is ‘unwilling or unable’ to take effective measures. The proposed six point criteria; informed by the inherent peace seeking spirit of the Charter, drawing insights from the Convention Relating to the Status of Refugees 1951 and the ICC Statute of the International Criminal Court 1998, would assist in determining the two limbs of the test: unwillingness and inability. Each limb has separate requirements and needs to be assessed separately starting with willingness, as an able state may not be willing to take necessary measures. The proposed criteria are that (i) there must be an armed attack or it is imminent against the victim state; (ii) the host state must show willingness by words and deeds; (iii) it must demonstrate military ability (immediate and long term) to stop or prevent the attack; (iv) a reasonable time should be allowed to the host state to effectively deal with the non-state actor; (v) ‘effectively’ dealing with the non-state actor/s includes political will and ability seeking a political solution; and (vi) if the host state does not have control over its entire territory, the victim state may use necessary and proportionate use of force in self-defence.
The attacks in Afghanistan by the armed groups based in Pakistan collectively constitute an armed attack triggering the use of force in self-defence. As Pakistan is willing and able to take measures against non-state actors, any US strikes inside Pakistan, without Pakistan’s consent, would be unlawful. The attacks in Pakistan by the Pakistani origin armed groups based in Afghanistan collectively constitute an armed attack and as Afghanistan is unable to take measures and lacks control in certain parts of Afghanistan, the Pakistani strikes inside Afghanistan (especially in the uncontrolled border areas) are lawful.
Shah, N. (2020). The 'Unable' and 'Unwilling' Test in International Law: the use of force against non-state actors in Pakistan and Afghanistan. In The Asian Yearbook of Human Rights and Humanitarian Law. Brill Academic Publishers. https://doi.org/10.1163/9789004431768