Nuestra NEBRIJA 35 - octubre 2020

37 to war in international society, although without much success. The World Wars had to happen for humanity to be convinced that war had to be prohibited, or its survival would be at stake. The United Nations Charter incorporated a series of regulations that strictly prohibited not only warfare, but any use of force, and devised a very complex and well-armed legal system in order to punish violations of those regulations. This system only contemplates two exceptions to the use of force: the institutional use by the United Nations Security Council to punish precisely violations of the rule, and self-defense, individual or collective, -regulated by Article 51 of the Charter-, whose content was also considered customary, that is, unwritten law that is formed on the basis of the repetition of actions in practice. According to this provision, States suffering an armed attack may use force to defend themselves from the aggressor, until the Security Council can deal with the situation. Self-defense is considered as an immanent right and can be exercised individually or collectively, for which some defensive alliances have historically been created, such as NATO, and the Warsaw Pact. After the 2007 Lisbon Treaty, the law of the European Union has also incorporated the obligation -set out in Article 42.7 of the European Union Treaty- of all Member States to help the State that has suffered armed aggression in its territory. Although the text of Article 51 of the United Nations Charter does not state that the author of the armed attack must be a State, for decades it was understood that this should be the case. However, after the 2001 terrorist attacks in the US, some States, the Security Council itself and NATO, considered that the US had the right to self-defense, despite the fact that the author of the attack had not been a State, but a terrorist group, Al-Qaeda. Following the Paris attacks in November 2015 by the self-proclaimed Islamic State, France also invoked its right to collective self-defense and called on its European partners to assist it under Article 42.7 of the EU Treaty in its fight against the Islamic State. As can be seen, the reaction of the United States in 2001, and afterwards that of the European states, does not conform to the usual interpretation of the right of self-defense contained in Article 51 of the United Nations Charter, which, let us remember, had also become customary. In order to legally qualify that reaction, we must understand either that a new custom is being formed -based on repeating events other than those contemplated in the text of article 51-, or that, at the time, in 2001, and then in 2015, international law was violated by the United States and its allies and after by the Member States of the European Union. We are at a decisive crossroads for the law that regulates the use of force and one of the most interesting developments in international law. On the other hand, not only does the right that regulates self-defense now seemobsolete because it does not adapt to the nature of the new actors in contemporary international society, such as terrorist groups, but also because the very nature of the attacks is entering a gray area of confusion. Think about whether a large cyberattack against a country is equivalent in severity and significance to a traditional armed attack. These developments are generating certain cracks in the rules that currently regulate self-defense in international law, which must be adequately studied by experts. Several professors from Nebrija University's Research Group on Security, Risk and Conflict Management (SEGERICO) are working on researching these aspects, -together with some of our PhD students in the doctorate that recently started in our University on these matters-; trying, as always, to answer society's questions and problems in each historical moment. L egitimate defense is considered as an immanent right and can be exercised individually or collectively