Of one mind about chemical weapons and protecting the innocent

From afar, the probable use of chemical weapons by the Syrian regime could seem like just more Middle East mayhem. Yet it is not. Which is why President Obama and other world leaders are contemplating stiff action in Syria based on evidence of at least one sarin-gas attack.

More than other tools of war, chemical weapons are indiscriminate in what they strike. Poisonous gases can float anywhere. They can wipe out entire populations of civilians, either by design or a change of wind. Even the weapon’s users might be hit.

For these reasons, nations have gradually agreed since 1899, or at the dawn of modern warfare, to tougher sanctions against these tools of destruction. In 1997, the Chemical Weapons Convention came into force with the support of 188 states.

This steady toughening of rules is not simply because of the immense fear such weapons evoke by their effects. It is because enough people have made a conscious choice to protect the innocent – or the very idea of innocence as the preferred condition of every human being.

As humanitarian scholar Hugo Slim wrote in a 2008 book about civilian protection, “The main idea behind limited war and its civilian ethic is, of course, that of limited killing. This is because every human being’s life is precious to themselves, to those who love them and, if one is religious, to God as well.”

As the United States and others now debate their next steps in Syria, this century-long progress toward a near-universal acceptance of protecting the innocent from an indiscriminate weapon should be a guiding principle.

Mr. Obama and others, of course, have strategic and tactical concerns. Would outside intervention cause even more use of chemical weapons? Would a foreign invasion lead to high civilian casualties? Can an over-indebted and war-weary Europe or US afford to act?

Even deciding who is a civilian is often difficult. The Geneva Conventions define civilians for what they are not – as not a warrior or someone directly helping a war. But what about a teacher of militant Islam? Or a teenage army conscript? What of the Syrian civilians who give bread to rebels?

And then there is the possibility that Syrian President Bashar al-Assad may have simply allowed a small chemical attack as a bargaining chip in possibly negotiating an end to this civil war.

Given the history of the Iraq invasion, Washington might not want to rely on its own evidence of gas having been used in Syria to lead a campaign for the United Nations to act. And the US has a mixed record of protecting civilians in war, although it is a record far better than that of its foes in recent wars.

As careful as the Obama administration has been in using predator drones to strike terrorists, for example, this aerial weapon is generally less effective than the use of soldiers on the ground in avoiding “collateral damage” to civilians.

Obama has described the use of chemical weapons by the Assad regime as a “game changer.” The killing of civilians with Syrian fighter jets and other conventional means – more than 70,000 – has not yet pushed the US or others to militarily intervene. But letting the regime break international norms on chemical weapons would set a big precedent and erode a global consensus on a major humanitarian rule of war.

Respect for innocent life lies at the heart of most rules of war. Not every intended wartime attack on civilians can be prevented. But some attacks matter far more than most. Knowing the principle at stake in chemical warfare should help world leaders make the right decision on Syria.