The legality of exercising self-defence against the non-state actors is one of the disputed concerns of the jus contra bellum. In the practice of states, the right to self-defense against non-state actors is increasingly invoked and accepted. Nevertheless, the recognition of this right must resolve a fundamental obstacle: that of explaining why the host state's rights, particularly its right to territorial sovereignty, are not infringed by the self-defensive force used within its territory.

When it comes to the states exercising self-defense against non-state actors, they rely on the host state's involvement with those actors to justify the use of force in the territory of that state.[1] In this article, the significance of the principle of necessity has also been illustrated that has to be considered while exercising the right of self-defence against the non-state actors. Moreover, the major problems that come up when the victim state exercises the right of self-defence against the non-state actors, have also been looked at.

The right of self-defence mentioned under article 51 of the United Nations Charter (UNC) acts as an exception to article 2(4) of the United Nations Charter which prohibits the use of force. The major concern that arises is that the bare text of article 51 talks about the right of self-defence against the acts of a state or against the state actors and this can be misused as a particular state can attack another through the help of a non-state actor, further encouraging terrorism. So, this article tries to analyze the existence this right of self-defence against such terrorist groups i.e. the non-state actors.

Introduction
Military and technological advancements and their availability to the private actors, has increased the destruction capacity of the non-state actors. This makes it the need of the hour to provide some attention to the concept of the non-state actors. Regrettably, the term only provides a negative definition, dissociating itself from the legally settled term the state.[2] The realization about how destructive the actions of these groups can be, has made it essential to emphasize on the right of self-defence[3] against them and to provide the states with the same right to defend the territorial integrity, sovereignty and political independence of their own state.

The point of self-defence becomes more severe when a particular state has been a victim of the threat possessed by these irregular armed groups, and the Security Council fails to take any action or to give power to these states to take any action.[4] The non-state actors by acting under the control of some states that give shelter to terrorism, impose threat on other states and carry out armed attacks in other states and thus breaching the sovereignty of the fellow states. There exist certain circumstances where it might be valid to not provide a particular state with the right of self-defence as the other state must have already acted in self-defence and this is to be noted that there definitely cannot be a right of self-defence against the right of self-defence.

The majority of the issues that come up while exercising self-defence against non-State actors, are centered around Article 51 of the United Nation Charter, either to demonstrate that the restrictive inter-State understanding is not supported by the language of the provision or intended by the drafters,[5] or to identify a different standard of attribution of the non-State actors' attack to the host State. The general notion says that article 51 may not restrict the right of self-defence against the non-state actors, but it eventually fails to draw a link between the host state and the victim state.

Sovereignty has been recognized by article 2(1) of the UNC and is a crucial aspect which must not be ignored or breached by the actions of any other state.[6] There are instances when this sovereignty is harmed by the acts of an irregular armed group. According to the International Commission on Intervention and State Sovereignty, sovereignty in the Westphalian sense of the word has come to mean the legal identity of a state in international law.[7] The right to self-defence hence turns out to be the most crucial weapon in order to defend the sovereignty of a particular state, which is to be addressed in this paper.

Which State's Territory May Be Used For Self-Defence Against Non-State Actors?

The initial idea of using justified force against the non-state actors is that this measure may be taken in the state where the latter might be found, i.e. the action must be taken in the territory of the state that is harboring the irregular armed groups. In support of this claim, there exist the United Nation Security Council Resolution 1373 that states "harbouring of terrorists as an action which constitutes a violation of international law".[8]

There are certain states that do not agree with this particular way and do not even identify the presence of these non-state actors or irregular armed groups. In order to deal with this situation, there exist the 'unwilling and unable' doctrine that eventually justifies the action of self-defence of one state on the territory of another state when the latter does not want or is unable to control or eliminate the risk evolving from the wrongful activities occurring on its territory.[9] Moreover, even in Lotus case, the Permanent Court of International Justice i.e. PCIJ held that every state is obligated to use due diligence so that it can prevent criminal activities originating from its territory against other states.[10]

This was further confirmed by the ICJ in the Corfu Channel case that every state has the obligation of not knowingly allowing its territory to be used in a way that endangers the rights of other states.[11]

The next issue that comes into the picture with respect to this is that certain terrorist groups are not associated with any particular state, i.e. these organizations are planned in one state, financed from another state, plan the attack in a third state and the attack takes place in the fourth state. The most prominent examples for the same are Al-Qaida that can be traced from Pakistan to Nigeria and Islamic State that can be found from Afghanistan to Mali. Another example of such an attack is the 9/11 where, as per the findings of the US-American secret services, the financing of the attack could be traced from Saudi Arabia whereas the cell that implemented this attack, was composed of Arab students that lived in Germany. If any particular stage of people is removed, then this crime would have been impossible, and it turns out that all the people involved were equally responsible and had their part to play. However, the government of Afghanistan claimed that there was no involvement of the government in this particular attack.

Talking about a way forward to this particular issue, the first thing that has to be kept in mind is the unjustified breach of the sovereignty of any state, i.e. the attack while exercising the right of self-defence must not be exercised in any state which was not aware of this activity and which didn't act as a shelter for the unlawful activities of the non-state actors. However, the right of self-defence can be eventually exercised against the non-state actors in the states where they are present in that particular moment, and the latter must also co-operate and help in locating these irregular armed groups. In simple words, the victim state must be justified in taking action against the non-state actors in order to eliminate future possibilities of such attacks.

Article 51 And The Concerns Of The Present World

Article 51 provides a state with the right of self-defence when there occurs an armed attack against it.[12] In most cases, this armed attack is carried out by a state. However, there exist certain unrecognized entities as well, so-called de facto regimes, may cause an armed attack. Article 51 lays down three conditions for a state to use force against some other state. Firstly, for exercising this right, the state must be under an armed attack. Secondly, the state must also report to the Security Council about the actions undertaken by it in order to defend itself and lastly, the state shall only use force after the Security Council has taken all such measures necessary to maintain international peace and security.[13]

Initially, the use of force while exercising the right of self-defence was justified only against a particular group and not against the non-state actors or irregular armed groups. Earlier, even the ICJ followed this state-centric approach as it denied Israel's claim to use of force under the right of self-defence against the terror attacks that originated from the Occupied territories in the case of Advisory Opinion on the Legal Consequences of the Construction of a Wall in the Occupied Palestinian Territory. The court eventually held that there were two reasons why Israel could not invoke the right of self-defence.

The first was because Israel didn't claim anywhere that there was any state behind these attacks, i.e. the claim did not mention any particular state that was attributable to this terror action.

The second was since the actions originated from a territory that was under the control of Israel, the Security Council resolutions 1363 and 1373 were not applicable.[14] However, at present there have been certain considerable state practices where the right of self-defence was justified against the irregular armed groups and the non-state actors as well. Such a practice was that of 9/11 and resolution no. 2249 of 20.11.2015 "concerning the activities of the Islamic State (ISIS) in relation to Iraq and Syria", in which the stand of the Security Council eventually justified the right of self-defence against the non-state actors.

There exists another concern at international stage i.e. whether the acts of only some certain groups can constitute an armed attack or the irregular, unarmed actions breaching the sovereignty, by any group can be termed as an armed attack. Isolated armed actions that take place in border areas cannot be termed as an armed attack whereas when there occurs an invasion by the armed forces as done by the ISIS into Iraq from Syria, the requirement of an armed attack is fulfilled, and the same can be termed as an armed attack.

The attribution to that state, from the territory of which the armed attack is being carried out, is not necessary. Because, if the territorial state intervenes and then stops the armed attack, in that case, no issue of attribution must arise because any attack by the victim state would not be proportional as the armed attack has already ended. But in circumstances where the armed attack is in continued, the right of self-defence comes into the picture.

The other major concerns include the term 'armed attack' not being defined by the UNC. However, the Charter uses the term 'aggression' under article 1 and 39. Yoram Dinstein has also argued that Article 51 of the Charter purposely uses the term 'armed attack' because the concept of an 'armed attack' is more restrictive than that of 'aggression'.

[15] 'Aggression' turns out to be a wider concept that eventually includes the threat of use of force,[16] but only the threat of an armed attack cannot trigger and justify the right of self-defence against the originator of that threat, and that is the very reason that the term 'aggression' has not been used in article 51 of the Charter. Antonio Cassesse has also stated in his work that an armed attack must include "massive armed aggression against the sovereignty, territorial integrity as well as the political independence of a particular state that imperils its life or government".[17]

In order to support the same, the judgement of Nicaragua v United States must be taken into consideration in which the ICJ held that "it will be necessary to distinguish the gravest forms of the use of force (those constituting an armed attack) from other less grave forms".[18]

Therefore, it is not necessary for an armed attack to be in the form of a massive military operation. The attacks that occur on a small scale and the 'low intensity' fights can also be termed or considered as an armed attack as the actions undertaken by the terrorist groups or insurgents are mostly not in the form of military attacks but these attacks have the capacity of taking away the lives of the civilians and military of that state.[19]

In the judgment of US vs Nicaragua of 1986, the International Court of Justice considered such covert armed actions could be classified as an armed attack if they are of sufficient gravity.[20] Thus it is valid to say that there exists no clear threshold of what constitutes an 'armed attack' and it must be decided from case to case basis whether the level of aggression that is used in that case, constitutes an armed attack or not.

What Matters Is The Armed Attack And Not The Attacker

It must be argued that the makers intentionally did not mention that the right of self-defence could only be exercised against the armed attack by a state and they were wise enough not to exclude the situations where the armed attack has been carried out by the non-state actors. That is the main reason why article 51 revolves around the victim state and not the attacker. If a particular state suffers from an armed attack, they have the right to respond irrespective of who the attacker is.

The initial justification that is also supported by the ICJ decisions in the Nicaragua case, the Wall advisory opinion and the Congo and Uganda cases, refers to the law on the responsibility of state especially the imputability of the non-state aggression acts to the state from where they act. To support the same, we also need to take article 21 of Articles on State Responsibility that justifies the measures taken as a right of self-defence and that measures taken against the originator of armed attack do not constitute the breach of international law.

Self-defence is an inherent right which can be exercised by a state whenever it faces an armed attack irrespective of the source or from where it originates and also irrespective of imputability to the third state. Taking the consent from the third state is not necessary if it has failed to take any preventive measure to curb the wrongful activities of the non-state actor.

The Security Council has also explicitly stated that "also attacks of non-State actors, not only those of states, may endanger international peace and security the measures provided for in Chapter VII including the right to self-defence may also be taken in case of an armed attack by a non-State actor".[21] Article 51 of the Charter of the United Nations (UN Charter) cannot be viewed in a vacuum, and it needs to be interpreted in light of State practice.[22]

But there are also certain instances when the host state is, in all possible ways, unable to take any restrictive action to curb the unlawful actions of the non-state actor operating from its country as the same happened in Lebanon in 2006, Mali in 2013 and in Somalia in 2008.[23] In that particular case, a state which eventually accepts its inability to guarantee the international security and also the internal security of its own state, can lastly fulfil its 'alienum non laedas'[24] obligation by extending itself to international cooperation. To summarize the same after considering the present state practices, the exercise of the right of self-defence can be justified against the armed attack caused by a non-state actor.

Necessity And Proportionality In The Use Of Force Against Non-State Actors

A lot of hardships have been faced while applying the principle of necessity and proportionality against the non-state actors. The principle lays down that the use of force must be in order to destroy or end the threat of attack, i.e. the use of force must be done only when the attack is ongoing or when there exists the threat of another future attack.[25]

Now coming to problem that is faced while exercising this right against the non-state actors is that the armed attacks carried out by these non-state actors either end and are not ongoing or there exist no imminent threat of attack as the attacks carried out by these groups may take more than 4-5 years of gap between the two attacks. But even after looking at this huge time difference, the imminence of an armed attack can still be proved by taking into consideration the intent possessed by a non-state actor and also its capabilities which include the weapons and other assets like the weapons of mass destruction or the capability possessed by the non-state actor to attack repeatedly on a state.

The intent can be derived from the statements made by the non-state actors and irregular armed groups. This capability of the non-state actors can be diminished by successfully acting in self-defence and curbing the menace of these non-state actors. Thus, a certain time frame is required with respect to the action of the defending state while exercising the right of self-defence against the non-state actor.[26]

And the same has been supported by the statement of Schmitt i.e. the mere fact that a terrorist group exists leads to the understanding that there will be a dispute because of there was no intention to continue the violence, the terrorist group would disband.[27]

The second point is that the use of force must be done only when the other alternatives, i.e. all the peaceful measures, have been exhausted but the problem faced with this is that it is almost impossible, in all circumstances, to indulge in any kind of peace talk or diplomatic relation with the non-state actors.[28]

And even if the state somehow gets in touch with these non-state actors, the demands possessed by these non-state actors are of extreme ends and the biggest example of the same was that of Al-Qaeda where their demand to negotiate was the complete withdrawal of the troops of the United States from the Middle east, and there should be an end to the support of America for Israel.[29] Hence, the actions taken by the victim state against a non-state actor must be justified as the right of self-defence in international law.

The principle of proportionality illustrates that the attack done acting under self-defence must correspond to the initial armed attack.[30] This is definitely not to be inferred from this that the weapons and technology used must also be similar.[31] However, it does mean that the defending state shall only the use the force that is needed to protect itself must use force that is proportional to the initial attack.[32]

Conclusion
To conclude, the use of force in self-defence against a non-state actor within the territory of another state is lawful in cases where the host state or state providing shelter to the non-state actors (including the terrorist groups) is unwilling to take preventive measures in order to curb the harmful activities of these non-state actors. The major concern in most of the circumstances is whether the activities of a non-state actor can constitute an armed attack or not and the answer to this is yes, taking into consideration the opinio juris and scholarly opinion which confirms that the actions of non-state actors can be termed as an 'armed attack'.

The victim state after exercising the right of self-defence and responding to the non-state actors, must inform the Security Council about the measures taken in order to justify itself and clarify that it intended to target the non-state actor only.

The use of force against the non-state actors has imposed a dilemma for the international law as it can definitely not be expected from the victim state to not respond to the breach of its sovereignty and the loss of lives in the state. On the other hand, the right of the host state also needs to be upheld. However, the state practices have turned this notion in favour of the victim state.

Thus, while exercising the right of self-defence what eventually matters is whether there has been an armed attack or not whereas the attacker or source is comparatively irrelevant and that every state has this right of protecting its sovereignty, territorial integrity and political independence. The limited-time that a defending state must provide the state from whose territory the non-state actor operates, depends on the imminence of the threat posed by that non-state actor. Hence, the right of self-defence under article 51 of the UNC very well exists against the non-state actors.

End-Notes:

1. Antonello Tancredi, Doctrinal Alternatives to Self-Defence Against Non-State, Zaorev de, 2017.
3. Brownlie�s Principles Of Public International Law 1090 (James Crawford eds., 8th ed. 2009).
4. U.N. Charter art. 51.
5. Michael Wood, Self-Defense Against Non-State Actors � A Practitioner�s View, Zaorev de (2017) https://www.zaoerv.de/77_2017/77_2017_1_a_75_77.pdf.
6. S. Murphy, Terrorism and the Concept of �Armed Attack� in Article 51 of the UN Charter, (2002) 43 Harv ILJ 42.
7. Olivier Corten, Has Practice Led to an �Agreement Between the Parties� Regarding the Interpretation of Article 51 of the UN Charter?, Zaorev de (2017) https://www.zaoerv.de/77_2017/77_2017_1_a_15_17.pdf/.
8. ICISS (2001) Responsibility to Protect, � 12.
9. United Nations Security resolution 1373 (2001), Security Council Counter Terrorism committee, https://www.un.org/sc/ctc/resources/databases/recommended-international-practices-codes-and-standards/united-nations-security-council-resolution-1373-2001/.
10. Ir�ne Couzigou, The Right to Self-Defence against Non-State Actors: Criteria of the �Unwilling or Unable� Test, Heidelberg Journal of International Law, 2017.
11. S.S. Lotus (Fr. v. Turk.), 1927 P.C.I.J. (ser. A) No. 10 (Sept. 7) � 269.
12. Corfu Channel, United Kingdom v Albania [1949] ICJ Rep 4 � 22.
13. The Charter Of United Nations: A Commentary 1416 (Bruno Simma et al. eds., 3rd ed. 2012) [hereinafter "The Commentary Of Charter"]; Federica I. Paddeu, Use of Force against Non-State Actors and the Circumstances Precluding Wrongfulness of Self-Defense, 30 Leiden J. Int�l L. 93,94 (2017)
14. V. Upeniece, Conditions for the lawful exercise of the right of self-defence in international law, EDP Sciences (2018) https://www.shs-conferences.org/articles/shsconf/pdf/2018/01/shsconf_shw2018_01008.pdf.
15. Advisory opinion concerning Legal Consequences of the Construction of a Wall in the Occupied Palestinian Territory, Advisory Opinion, 2004 I.C.J. 136 � 139 (July 9).
16. YORAM DINSTEIN, WAR, AGGRESSION AND SELF-DEFENCE, 167 (Cambridge University Press 3d ed. 2001)
17. G.A. Res. 3314 (XXIX), Definition of Aggression (Dec. 14, 1974).
18. Antonio Cassese �International law� (2nd edn Oxford University Press 2015), Cassesse (2005) p.354
19. Military and Paramilitary Activities in and against Nicaragua (Nicar. v. U.S.), Judgement, 1986 I.C.J. 14 (June 27) [hereinafter �Nicaragua case�].
20. Marco Sass�li, The Notion of Armed Attack under the UN Charter and the Notion of International Armed Conflict � Interrelated or Distinct?, Geneva Academy,
21. 2014, http://www.prix-henry-dunant.org/wp-content/uploads/2014_IRMAKKESEN_Paper.pdf
22. The Commentary Of Charter, supra note 12, at 1415.
23. S.C. Res. 1373 (Sept. 28,2001); S.C. Res.1368 (2001).
24. M. Wood, The Use of Force in 2015 with Particular Reference to Syria, Hebrew University, Jerusalem, 5.11.2019, Hebrew University of Jerusalem Legal Studies Research Paper Series No. 16-05), http://papers.ssrn.com.
25. supra note 1
26. Jutta Brunn�e, Sic utere tuo ut alienum non laedas, Oxford Public International Law (2010).
27. KN Trapp, �Back to Basics: Necessity, Proportionality, and the Right of Self-Defence against Non-State Terrorist Actors� (2007) 56 ICLQ 141.
28. Ryan Manton, Necessity in International law, Hilary Term, 2016.
29. Schmitt (2007) p.175
30. Edmarverson A. Santos,The right to self-defense in International Law, Inllaw, https://inllaw.com/the-right-to-self-defence-in-international-law/.
31. James F. Jeffrey & Michael Eisenstadt, U.S. Military Engagement In The Broader Middle East, The Washington Institute for Near East Policy (2016) https://www.washingtoninstitute.org/uploads/Documents/pubs/PolicyFocus143_JeffreyEisen-4.pdf
32. Judith Gardam, Necessity, Proportionality and the Use of Force by States, Cambridge University Press (2004) 5.
33. C. Tams, The Use of Force against Terrorists, EJIL 20 (2009), 384
34. KN Trapp, �Back to Basics: Necessity, Proportionality, and the Right of Self-Defence against Non-State Terrorist Actors� (2007) 56 ICLQ 141.