We’ve seen these images before.

Photographs of victors posing with the corpses of their enemies. Photographs of the vanquished subjected to posthumous humiliation.

We’ve seen these images before. From Iraq and Afghanistan. From Bosnia and Berlin. Rwanda and Darfur. Okinawa and Vietnam.

No matter the war, no matter the perpetrator, what comes across in these photographs is almost always the same: They capture a moment where the humanity of both the living and the dead is absent.

War dehumanizes, desensitizes. It can break the spirits of great men and create monsters of schoolboys. And the history of warfare is accompanied by a history of trophy taking and desecration.

So, why are we still surprised?

The publication on Wednesday of photographs of American troops in Afghanistan posing with pictures of enemy corpses was the latest in a series of similarly grisly embarrassments for the United States. American leaders apologized for the photographs, which were taken in 2010, as they sought to contain the diplomatic and political fallout from the incident. Everyone expressed appropriate outrage.

But, however abhorrent these actions by a small group of American forces in Afghanistan are, they are in keeping with the history of conflict. Perhaps we’re surprised because we think we’re more civilized than we are. Or because most of us don’t actually understand what war is.

This war is 7,000 miles away, but its images can reach us in seconds. Many of the gory pictures are tweeted on Twitter. Or liked on Facebook. Or unliked. A great disconnect exists between the horror of the photographs and the nifty devices and platforms we can click on and off to control our access to war. War is the most antisocial of human activities, yet Afghanistan — and maybe all wars from now on — will be experienced by most of us through social media, in the palm of our hand. From a distance, we’ll see war up-close.

“Americans imagine war being much cleaner than it is,” says Jennie Kiesling, professor of history at the U.S. Military Academy at West Point. “We’re fairly ignorant of war, so when we see these dreadful things, we think they’re unusual when they’re actually not.”

These dreadful things have been around for a while.

“It goes back to the beginning of time,” says Wayne Lee, professor of history at the University of North Carolina at Chapel Hill and author of “Barbarians and Brothers: Anglo-American Warfare, 1500-1865.” “We have examples of paleolithic skulls that have been shaped into a drinking cup” to signify vanquishing of the enemy.

From the tale in Greek mythology of an enraged Achilles dragging the body of Hector around the walls of Troy to Somali fighters parading the bodies of American troops in Mogadishu in 1993, examples abound in literature and history of the vengeful acts of warriors.

Lee tells the story of Continental Army soldiers who were taken to a battleground in Wyoming, Pa., and shown the remains of soldiers who had been scalped and mutilated. They avenged this act a couple of weeks later in Newtown, N.Y., by skinning the legs of two dead Native Americans and turning them into boots.

In World War II, the collection and curation of body parts, especially from the Pacific, were common, and human remains were often shipped home through the mail. Skulls and teeth were particular favorites. Germans made souvenirs from the remains of dead prisoners in concentration camps.

The misuse of a body to commemorate what one has accomplished on the battlefield or to intimidate your enemy is deeply embedded in the human psyche, Lee says. Victorious warriors were celebrated for displaying the spoils of war, including scalps and skulls and heads on a pike.

“It gets interesting when you have cultural mores that go against this,” Lee says. “Society agrees that it is unacceptable, and so you start getting rules about how you should treat the enemy.”

But even the rules — even the widespread agreement that “This is not who we are,” as Defense Secretary Leon E. Panetta said on Wednesday — can only stop so much from happening.

The impulse of soldiers to photograph their dead enemies is driven by a number of factors, says Nancy Sherman, author of “The Untold War: Inside the Hearts, Minds, and Souls of Our Soldiers” and a professor of philosophy at Georgetown specializing in the ethics of war.

“There’s relief that they’re alive and not dead. There’s also top-dog exuberance and pent-up revenge,” she says. Another factor, especially in places such as Afghanistan, is when these incidents take place among units that are operating in remote locations, she says.

“There often isn’t adequate leadership,” Sherman says. “They need people reminding them and telling them that this isn’t how good soldiers respond. A lot of this goes to command culture, and the absence of it is what is apparent.”

Lee agrees that these incidents come about at “moments in which normal sense of controls have slipped. But [in today’s military] it needs to be emphasized that this is a real minority.”

So it is right that we are outraged. Horrified. Shaken. But there’s no reason we should still be surprised.