Evidence is mounting of possible war crimes by Russia and, on a vastly smaller scale, by Ukraine. We can be sure, given that every act of warring nations is documented on social media today, that the truth will come out. But where did the idea come from that some ways of fighting wars crossed some sort of civilized line? Who decided where that line should be drawn? Where did the very notion of "war crimes" come from?

Union Major General Sherman, the general behind the infamous Sherman's March during the Civil War, famously said that "War is hell." International laws on war crimes are a historically recent innovation intended to mitigate how terrible and devastating war becomes. They are attempts to prevent war from descending entirely into hell, especially for non-combatants.

In the West, the primary sources for laws governing how war should be waged are found in Just War Theory. The earliest idea that war should be governed and moderated, however, dates long before any formal formulation of Just War Theory. In Deuteronomy 20, Moses instructed the Israelites not to kill the women and children of their enemies.

Much later, the Roman Republic would embrace three criteria for waging war: first, that it had to be waged for a legally sound reason, such as in response to aggression; second, that it had to be declared by someone legally authorized to do so; and third, that it had to be waged justly. As ethically innovative as that may sound, the Romans still had no problem using horrific tactics, such as rape, torture, enslavement, and terrorism, in their warfare.

It was Christian thinkers, especially Augustine of Hippo and Thomas Aquinas, who most fully developed the ideas governing if and how war was to be waged. This Judeo-Christian approach eventually influenced the formation of the code of chivalry in Medieval Europe. Like the injunctions in Deuteronomy 20, the code was eventually expanded to include the protection of women and non-combatants, with the ideal of the knight being a protector of the weak. Though in the throes of war, these ideals were rarely followed, the code held among the nobles. For example, if a knight unnecessarily killed another knight in combat, he could be charged with murder. This was not considered a war crime, however.

In the wake of the brutality of the Spanish conquests in the Americas, thinkers such as 16th century Spanish theologian and jurist Francisco de Vitoria began to argue that war was never part of God's plan and could only be justified on the grounds of the common good. Thus, consideration of war and warfare shifted from a topic within theology to the emerging realm of international law.

At the same time, the emergence of gunpowder armies and other military technologies made war increasingly destructive. As weapons became more powerful, the ability of armies to target civilians grew as well. This led to legal attempts in the 19th century to restrict warfare.

The first international treaty on warfare was the 1864 Geneva Convention, which covered the treatment of sick and wounded prisoners of war. This was followed by the Hague Conventions of 1899 and 1907, which also banned weapons such as poison gas, the killing of surrendering prisoners, looting, and the bombardment of undefended towns. The 1925 Geneva Protocol supplemented the ban on chemical weapons with a ban on biological weapons. Protections afforded to civilians were expanded in the 1949 Geneva Conventions. In 2008, the U.N. Security Council added rape and sexual violence to the list of war crimes.

Although a few Germans were tried for war crimes after the first World War I, it was the Nuremberg Trials and the lesser known International Military Tribunal for the Far East after World War II that most fully established the idea of war crimes and holding violators accountable. Since 2002, such trials have been handled by the International Criminal Court in The Hague. In the U.S., war crimes can be prosecuted using the 1996 War Crimes Act and the Uniform Code of Military Justice.

Despite all the conventions, treaties, and laws, war crimes continue to be a part of every military conflict and are often perpetrated by all sides. Heads of state and others have been prosecuted, from a range of countries, while others have escaped accountability altogether. It is important to remember that the U.S. has been guilty of war crimes, such as the violations at Abu Ghraib prison in Iraq.

The very concept of war crimes is rooted in the Judeo-Christian understanding that in a deeply flawed world, war is at times a horrible necessity. However, the desired ends of nations, even if noble, do not justify the means. The waging of war, even if just, must not violate the inherent dignity of human beings. In other words, all is not fair in love and war, and to whatever extent we can control, war should not be hell.