1. IntroductionIn recent years, one of the old, yet controversial doctrines of the law of neutrality -called "unwilling" and "unable"[1] doctrine- has been reformulated in the jus ad bellum discourse, according to which some states may use force in self-defense against non-state terrorist actors operating within the territory of host states based on the unwillingness or inability of the territorial state to control them. The unwilling or unable doctrine has one of the lowest standards with which it determines when non-state terrorist organizations can legally be attacked in third states based on the right of self-defense,[2] even though the legality of such use of force against non-state actors in weak host states, without the consent of the host state, is unclear. In the context of legal positivism, this article seeks to prove whether the current sources of international law allow states to recourse to the unwilling or unable doctrine in the host state. Since these concepts have not been mentioned in any legal document (besides Article 17 of the Rome Statute and the 1951 Refugee Convention) or even international case law, it is not clear whether it is possible to accept such use of force in international law despite its prohibition in the UN Charter, denying its legitimacy by most publicists, very little occurrence of it in the practice of states and subjectivity of the concept of unwillingness or inability. The International Court of Justice and some scholars also deny the legality of the use of force in an ineffective host.This article seeks to critically examine and demonstrate the evolution of the use of force in the name of self-defense against non-state actors in the territory of host states, which is justified by the unwilling and unable doctrine. The purpose of this research is not only to identify the unwilling and unable doctrine but also to offer a practical solution to the challenges regarding extra-territorial self-defense against non-state terrorist organizations.Research Question(s)This article, by examining de lege lata, seeks to verify whether treaties, customary laws, and international judicial practice allow states to legally resort to the unwilling and unable doctrine in another state (the host state). In other words, has the unwilling and unable doctrine become a part of international law (as it exists)? Moreover, does the doctrine provide a legitimate way to use transnational self-defense against non-state actors, particularly in a situation where the host state is willing to repress the non-state actors but is unable to do so? Based on which criteria is it determined that the host state is unwilling or unable to fight the threat posed by the non-state actors? Finally, is it possible for the acting state to make this decision unilaterally or does the host state also play a role in this regard? MethodologyThe article has used descriptive and analytical research methods. The necessary data has been collected through the library research method by reference to relevant books, essays, and international judicial decisions. FindingsThis article shows that although the right to self-defense in ineffective host states may be desirable in light of the contemporary security and safety threats, the existing data about the doctrine is incomplete and has many gaps. The "unwilling" and "unable" doctrine presents a significant challenge to the “rule of law” in international law. This doctrine based on self-judgment theories in international law and providing exceptions to the jus ad bellum regime, not only leads to the instability of this regime, but also its legal justifications are a serious attack on the fundamental legal concepts that are generally accepted in international law. This article, with a legal positivist look, believes that any resort to the "unwilling and unable” doctrine is subject to the following criteria: an armed attack according to Article 51 of the Charter, lack of control of the host state over its territory, proof of inability and unwillingness of the host state by the victim state, act of the victim state with the consent and cooperation of the host state, giving the host state a reasonable time to effectively deal with the non-state actor, and the inability of the host state based on duty of due diligence, lack of cooperation by the host state and refusal to accept international assistance. ConclusionAccording to the above, the inevitable conclusion is that it’s very difficult to balance the unwilling or unable doctrine with the jus ad bellum regime. This doctrine lacks both a legal underpinning and a clear, distinct content. The criteria for the unwillingness and inability, the legality of self-defense, and the permissibility of resorting to force in an ineffective host state do not have a valid basis in either treaty law or customary international law; It is not mentioned in Article 51 of the UN Charter, nor have the states accepted it sufficiently. The International Court of Justice and the most highly-qualified publicists have also refused to recognize such use of force. Due to the change in the nature and power of terrorist organizations, the rules in this field remain unclear and this field is replete with legal uncertainty. It is not surprising that the UN charter is not able to provide clear answers for these situations.Despite the relative success of the jus ad bellum regime in preventing armed conflicts between states, the mentioned doctrine undermines the legal framework regulating prohibition on the use of force and poses a threat to the UN Collective Security System. The doctrine distorts the concept of imminence and damages the definition of armed attack[3] 3 enshrined in Article 51 of the UN Charter by lowering the threshold for the justifiable use of force in self-defense. It also destabilizes the fundamental principle of necessity in self-defense. Finally, by providing weak governing standards for the victim state may make unilateral decisions as to the necessity of the use of force, in spite of the disapproval or unwillingness of the host state, the doctrine extremely over-privileges the interests of the powerful states at the expense of the rights and interests of typically weaker host states. Consequently, it should be acknowledged that the doctrine created to address the limited and specific threat of transnational terrorism cannot be a justification for weakening the regime designed to maintain international peace and security.If we apply this doctrine, any state will be allowed to start military operations simply on the pretext of the host state’s inability to suppress a terrorist group. Accepting to such a view by the international community and allowing to create this new legal order will lead to a fundamental change in the UN system if it is not completely damaged. By granting discretion to any state to adopt unilateral actions in the war on terror, through the unwilling and unable test, it simply ignores some fundamental provisions of the Charter (Article 39) and challenges the entire Collective Security System of the Charter. Creating unwritten exceptions to the principle that prohibits the use of force not only causes problems for the integrity of international law but also leads to disorganization in international law.Finally, within the framework of the lex lata, the only point that can be said regarding self-defense against attacks by non-state actors in situations, lower than the threshold that the ICJ has stated in the Nicaragua case, is that such actions are undoubtedly illegal. In the framework of the Lex ferenda, we believe that the customary law is evolving regarding the applications of Article 51 of the UN Charter, defensive action in the territory of target states, and the use of force against non-state actors in host states. Even in the light of Lex ferenda, it cannot be said that the unwilling and unable doctrine is currently an established rule of international law.[1]. Ashley Deeks, “Unwilling or Unable: Toward a Normative Framework for Extraterritorial Self-Defense”, Virginia Journal of International Law, Vol. 52, (2012), at 483,505.[2]. Sjöstedt Britta, “Applying the Unable/Unwilling State Doctrine – Can a State Be Unable to Take Action?”, Heidelberg Journal of International Law, Vol. 77, (2017), at 39.[3]. Craig Martin, “Challenging and Refining the Unwilling or Unable Doctrine”, Vanderbilt Journal of Transnational Law, Vol. 52, (2019), at 460.