This paper analyzes, on the one hand, elements of moral philosophy that provide background to understand the causes of war and its relationship with the exercise of power. On the other hand, it provides an overview of the current international legal system, suggesting the need to reformulate the institutional system to ensure the principle of non-use of war. Both philosophical and legal elements show that the phenomenon of war cannot be eradicated. And there is also a need to rethink the rules that organize international power around the monopoly of institutional force.