Loving the Battle of Blackwater week, Steven!! Do you consider Tyrion’s use of the wildfire to be a war crime?

Maybe. I take PoorQuentyn’s point that it was a purely military strategy aimed at purely military targets. But that doesn’t necessarily mean something isn’t considered a war crime. Weapons that cause “superfluous injury or unnecessary suffering” are considered war crimes, sometimes depending on how they are used. At various times, this has included crossbows, weapons with barbed or serrated edges, explosive or expanding bullets, poison, biological or chemical weapons,  nuclear weapons, and incendiary weapons. 

Now, whether Westeros includes that in their conception of the laws of war, I don’t know. But if Stannis had won the Battle of Blackwater, I could see him prosecuting Tyrion for murdering thousands of helpless sailors on both sides.