 Let me trace back the long legal evolution that led to the prohibition to use force and tried today in article 2, paragraph 4 of the UN Charter. War has been with humanity since time immemorial, and many thinkers and philosophers from all continents and traditions have reflected upon it. And in the western world, theologians have greatly influenced the thinking about war through the just war theory, and notably by Thomas Aquinas in the 13th century. And there is no need to delve into the distinction between just and unjust wars, but it is important to realize that by conditioning the righteousness of war to the fact that it be waged by an autoritas principis, that is a public authority, the just war theory has significantly contributed to the centralization of power through princes and kings and reduced the authority of vassals who were deprived of the right to wage war on their own. In other words, just war theory was distinctively constitutional in essence, of course by requiring also that the war be waged for a just purpose and with a right intention, the just war theory intended to limit collective violence between men. But those additional conditions were also very much constitutional in nature, because the just war theory was primarily designed to provide princes and monarchs with a roadmap as to when they could, without fearing God's judgment, when they could require from their own soldiers to go and kill the enemy or to go and die in the hands of the enemy. The just war theory was not so much concerned with the issue of wrongly causing harm to others, but to a very large extent it was centered about the ultimate moral dilemma that any head of state still faces today when engaging troops in a foreign war. What are the good reasons entitling the supreme commander to ask from his soldier not only that they be killed, but also that they kill other fellow human beings? And in medieval times, even if you survive the war killing others, or other Christians at least, without a good reason, was a sin accountable to God, and so was on the part of the king ordering to kill without a just cause. In the western world, the sovereign state became the only authority to resort to war, and because it was considered as a sovereign authority questioning the purpose of the war or the intention to wage it was said to be contrary to the very notion of sovereignty. Therefore, any war was irrefutably presumed to be just on both sides. Saying that war is necessarily just on both sides, waters down the just war theory and reduces it to nothing. War became a sovereign attribute of states, and states were free to resort to war. However, this did not mean that war was not regulated to a certain extent. States were free to wage war, they had the right to go to war, that is a use at bellum, but the way war was waged became increasingly regulated. What was called the laws of war, or use in bellum, or today international humanitarian law, progressively developed to protect wounded combatants, prisoners of war, together with civilians that were not taking part in the hostilities. Weapons inflicting unnecessary wounds were banned, while the distinction between military and civilian targets imposed to discriminate during the conduct of operations. All those developments are of course still very much with us today the law of armed conflicts. But due to the lack of time, it is impossible to go into details in that regard, and this course will not cover international humanitarian law. But I'm sure you know that international humanitarian law is a very important field of international law today, and that institutions like the International Committee of the Red Cross or the Red Crescent and the International Criminal Court, those institutions play a crucial role in trying to safeguard those rules of humanity. Leaving aside use in bellum and coming back to use at bellum, two first limitations on the absolute freedom of states to wage war came as a result of the 1907 Hague Peace Conference. From week 7, you may remember that the Hague Conferences further codified pacific means of dispute settlement and established the Permanent Court of Arbitration. During the 1907 Hague Peace Conference, two conventions were concluded that limited the use at bellum of states. The first convention, which deserves to be mentioned, relates to the opening of hostilities. The convention imposes on its parties to make a formal declaration of war when opening hostilities. And this is purely formal and procedural. It is just a procedural step, which does not really limit the right to wage war. But it conditions war upon such public formality. And it is rather quizzical to note that the preamble of the convention reads as follows. And I quote, considering that it is important in order to ensure the maintenance of pacific relations, that hostilities should not commence without previous warning. End of quote. War, peace and neutrality were three different states or legal statuses, each with different rights and duties, and it was possible to shift from the state of peace to the state of war through a formal declaration of war. The second convention, which deserves to be mentioned, is more substantial and it relates to the prohibition to use force, I quote, for the recovery of contract debts claimed from the government of one country by the government of another country as being due to its nationals. End of quote. That convention is often referred to as the Drago-Porter convention, as it is named after the Argentinian minister of foreign affairs, Luis María Drago, and the U.S. representative to the Hague Conference and former soldier Horace Porter. The idea that states should not be authorized to use force to recover contractual debt was first suggested by Carlos Calvo, a famous Argentinian international law scholar. Calvo reacted by this proposal to the naval blockade or gunboat diplomacy imposed by the U.K., Germany and Italy on Venezuela when it could not pay back its debts in 1902. And all this seems just incredible today, but those were the days. There was a time when it was perfectly legal to make a country pay its contractual debts by waging war against it. However, at the beginning of the 20th century, the morality of such policy began to be questioned. And that is why an agreement was found in 1907 to prohibit the use of force for that purpose. The Drago-Porter convention was thus the first substantial limitation on the freedom of states to use force. However, it only concerned a certain category of contractual debts, and furthermore, it was explicitly conditional. If the debtor country did not accept to go to arbitration over its debts or did not faithfully conduct the arbitral proceedings or did not implement the award, the creditor state would be free again to resort to the use of force. In other words, the Drago-Porter renunciation to use force for a limited purpose was based on a quid pro quo and reflected the reciprocity which is so much inherent in international law, as it is for instance reflected in the exceptional and aplenty contractuals of the law of treaties that we studied. Let us turn now to the legal developments that followed the First World War, and that will be taken in the next video.