During his teaching stint at a Dutch naval cadet school in the 1950s and '60s, Frits Kalshoven taught aspiring officers about how to fight a war as humanely as possible.

"In my whole teaching life, I have been telling all my students that they should not do certain things in war and why they shouldn't," Kalshoven, 73, a professor emeritus of international humanitarian law at the University of Leiden, said in a recent interview. "War between human beings has to be conducted, if it has to be conducted, in such a way that human beings remain human beings."

International humanitarian law was born to "mitigate the horrendous effects of war," he said. To that end, conventions have banned nations from engaging in certain acts, such as mistreating POWs and infringing on the right to life and personal property of people in occupied territories.