It’s the wrong metric.
My claim was not “most killings by the military are war crimes”, it was “war crimes going unpunished is a routine event”. The comparison is not “what percentage of the killing was unlawful?”, it’s “of the unlawful killings committed, what percentage go unpunished?”.
For both military and police, it’s “almost all of them”. Prosecutions are rare, and meaningful punishment is even rarer.
Most war crimes go undetected: the victims are unable to report them on account of being dead. Militaries also tend to be strongly disinclined to make any serious effort at discovering crimes by their own side; it’s not as if they actively investigate every killing.
Even when a war crime is detected and investigated, justice is very rarely delivered. See My Lai, see Haditha, see No Gun Ri, see Abu Ghraib, see the still unpunished torture regime of the Bush years. Given the obvious contempt for justice in response to the high profile massacres, why do you think they’d do any better for the crimes that are out of the media spotlight?
Every factor that allows police to get away with murder is also in effect for the military, often to a much stronger degree. The only people whose lives are worth less to the US authorities than American people of colour are non-American people of colour.
It’s obviously not the sort of thing in which hard numbers are readily available, particularly for wars that are still ongoing. But there is a mountain of qualitative evidence to suggest that unpunished war crimes are a very common occurence.
For example:
Or this book:
Note that my claim is not that US soldiers are notably worse than other soldiers. Pretty much every honest war memoir in print, regardless of nationality, contains some mention of unpunished war crimes.
Soldiers in action will commit war crimes; this is pretty much inevitable. Young men, trained to celebrate violence, placed under extreme stress, facing people who they are encouraged to dehumanise (and who are often racially and culturally distant from them), will predictably do horrific things. Not all of them, but some of them.
You can reduce the incidence of war crimes by (a) stomping the perpetrators hard when they occur, and (b) not deploying military force unless there is no other option. The fact that atrocities are an apparently inevitable part of war needs to be part of the calculation when evaluating the cost of military action.
The US is a notable failure at (a) as well as (b), and has been throughout its history.