Shortly after 8 p.m. on May 4, American B-1 bombers began pounding the Afghan village of Granai in an effort to protect a group of Afghan soldiers who had come under fire. When the air strikes ended seven hours later, somewhere between 26 and 140 Afghan civilians were dead (depending on whose figures you believe). The casualties added fuel to an anguished debate about civilian deaths in wartime that has raged since the war in Afghanistan began. Below, some questions and answers on the rules of war.

Question: How many civilians are being killed in Afghanistan?

Answer: The Brookings Institution concludes in its “Afghanistan Index” that more than 5,000 civilians have died in the war between 2006 and the first half of 2009. Nearly 2,000 of the deaths are attributed to pro-government forces, including the United States, other international forces and the Afghan army.

Q: How do those numbers compare with other conflicts?

A: Frankly, they’re low. In the same period in Iraq, for instance, more than 60,000 civilians were killed (as a result of military actions by all the parties in the conflict), according to Brookings.

Certainly, the number of civilians who have died in Afghanistan is tiny compared with the number in previous conflicts the United States has been involved in. Civilian deaths during the Vietnam War, for instance, were estimated to be in the millions, helped along by such atrocities as the massacre of between 300 and 500 villagers by U.S. soldiers in My Lai in 1968, and by carpet bombings of the countryside that indiscriminately killed whoever was below.

In World War II, nearly 40 million noncombatants were killed, according to historian Niall Ferguson, thanks, among other things, to the mass starvation tactics adopted by the Germans on the Eastern Front, the devastating firebombing by the Allies of Japanese and German cities, and the bombs dropped at Hiroshima and Nagasaki in August 1945.

Q: Why so many fewer this time?

A: War is different today. Precision weapons — smart bombs, Predator drones, and the like — make it possible both to identify targets and to hit them with more accuracy and less guesswork. Also, military leaders, politicians, the media, and the public are more sensitive to the issue, in part because the rules of war have evolved.

Q: So we should be pleased by the lower civilian death toll?

A: Not at all. The killing of innocent noncombatants remains a serious problem not just morally but strategically as well. The new U.S. commander in Afghanistan, Lt. Gen. Stanley McChrystal, acknowledged as much after Granai, saying that reducing civilian casualties is “essential to our credibility” with the Afghan people and issuing new orders limiting the use of air strikes. Since then, however, more civilians have died.

Q: But isn’t that what war is all about — killing and maiming more of them than they can kill and maim of you?

A: That’s what was believed for most of man’s existence. From the beginning of history until the 17th century, armies were free — ethically as well as legally — to kill, wound, or enslave as many members of an enemy’s civilian population as they chose. This was simply the nature of war.

Things began to change with the Thirty Years’ War. That conflict, which ended in 1648, was so devastating to what is now Germany that European leaders finally began to consider whether war should be not between entire populations but between armies. The shock and revulsion felt across the Continent caused the Dutch jurist Hugo Grotius to start developing rules of engagement that included distinctions between combatants and noncombatants.