Why can’t the hunger of the civilian population be used as a means of war?

Although people cannot completely stop wars and switch to another, more diplomatic and humane way of resolving conflicts, at least they are trying to influence the course of hostilities, making them more humane. For this, there is international humanitarian law, which regulates the behavior of the military and authorities during war. The civilian population does not belong to the war, they are not participants in these events, but victims, therefore the use of any kind of violence against the civilian population is considered inhumane.