There is a lot in this argument, and it is hard to do it justice in a short summary, but what particularly interests me is how the criminal law becomes part of this story.
According to Whitman, from the late nineteenth-century, humanitarian campaigners began to try and limit the horrors of war through the introduction of prohibitions on certain kinds of conduct - ensuring that survivors could not be killed or looted, introducing rules about the recognition of combatants and non-combatants and the limits of proper behavior in war. These kind of prohibitions now make up a substantial part of the modern law of war, as well as being linked to forms of international crime, such as crimes against humanity. While these are surely a great advance, Whitman questions the limits of the criminal law in this area. There are two aspects to this (and here the argument is my reconstruction of what I thought Whitman said, so may not be entirely accurate). First, it is not clear how useful or effective criminal law can be in a war situation, where you are dealing with scared or brutalized individuals. To be sure, these laws might provide for some limited redress afterwards, but we should be wary of claims that the law can guide conduct in war situations. Second, Whitman points out that this individualizes the law of war: it is no longer concerned with regulating conflicts between states, but with trying to determine just outcomes for individuals. The consequence of this is that the criminal law gets wrapped up in attempt to sanitize or humanize war. There are many reasons might we might want to do this - though better yet to avoid it altogether - but it is worth reflecting on whether the criminal law is an appropriate tool for for achieving these ends, or worse still, whether through this exercise we end up legitimating further violence.