Nonetheless, in modern warfare, the need to protect civilians is in constant tension with the desire to destroy the enemy. Getting that balance right has been a rocky process, with one mistake after another jolting U.S. policymakers into improving the way the military deals with civilian harm…

If American leaders abandon the war-fighting model they ultimately adopted in Afghanistan and Iraq, they may find it harder to counter a more brutal and cynical narrative about the best way to win a war — one that treats civilians as irrelevant.

In 2009, the Sri Lankan military cornered an estimated 5,000 or more Tamil Tiger insurgents on a narrow strip of land, alongside hundreds of thousands of uprooted civilians. By shelling the area indiscriminately and summarily executing the group’s escaping leaders, the government wiped out the insurgents — and killed tens of thousands of civilians in the process. Just like Russia’s brutal war in Chechnya during the first decade of this century, Sri Lanka’s campaign proved that if a government is willing to expel aid groups and journalists and employ indiscriminate force, it can defeat insurgents.

To make matters worse, Sri Lanka has been actively promoting its model abroad: since 1999, its leaders have been traveling to other countries facing domestic insurgencies, including Myanmar (also called Burma), Pakistan, and the Philippines, to share the lessons of their victory. They have staged annual defense seminars attended by military officers from across the world. Sri Lanka’s lethal counterinsurgency strategy requires having a strong stomach for civilian bloodshed and turning a blind eye to international criticism. But there are countries willing to go this route, because it can work. As one of the world’s leading exporters of military ethos, aid, and training, the United States can and should provide a counterweight.