One only has to look into the history of international relations to realize that the use of force has been intrinsically related to the ius gentium. For example, it is quite revealing that international law, as a scientific discipline, emerged from this relation. There are also many publications from the founding fathers that are related to this branch of law and which tittles specifically mentioned the law in war. To this end, one can relate to the works of De Vitoria, Suarez, Molina, Grotius, etc. Thus, it would not be too bold to claim that the modern international order was born from the regulation of the use of force and so, since the Renaissance.
The banishment of the use of force in international relations surely is the cornerstone of the United Nations Charter (hereinafter: UNC), this new social contract that would now exist between the nations that had defeated the Nazi-fascist barbarism and the Japanese imperialism. Yet, this rule, true and veritable idea that it was, did not emerge overnight but was the fruit of a long and laborious process from different stages of which will be presented in the following pages. It is fair to wonder how did we get to the current framework of the use of force and more specifically how States, those who are the very legislators of international law, have supplanted the law regulating the use of force; ius ad bellum, by the law on the prevention of war; ius contra bellum. Was it not Clausewitz who once claimed that war was nothing else but the extension of politics by other means, therefore being considered like any other (lawful) means and moreover, a sovereign right of States?
Once one knows the end point of this process, the UNC in its article 2§4, one can also wonder what were the steps of its development. The various phases that have shaped this process are of course diverse. Hence, according to inevitable and inexcusable historical and legal shortcuts, five general phases will be drawn from the evolution of the law on the prevention of war. Traditionally, the first phase corresponds to the doctrine of the just war.