Gas masks used on the Western front during World War I.
According to the United Nations, the Syrian civil war has already claimed over 60,000 lives. Yet it is not these deaths -- however tragic -- but rather the use of chemical weapons that the United States has identified as the threshold beyond which the Syrian regime's conduct will become intolerable. "The use of chemical weapons is and would be totally unacceptable," President Barack Obama said, addressing Syrian President Bashar al-Assad, on December 3, 2012. "If you make the tragic mistake of using these weapons, there will be consequences and you will be held accountable." The same day, Secretary of State Hillary Clinton sounded similarly grave warnings, stating that the use of chemical weapons "is a red line for the United States."
Now, with reports surfacing that the Syrian regime may have used a substance known as Agent 15 (a hallucinogenic chemical) in an attack last December, it is worth examining why countries such as the United States have singled out the use of chemical weapons as uniquely intolerable -- and what it will mean if Washington does not live up to its word and respond to Assad's attack with serious countermeasures.
Some history is in order. The Chemical Weapons Convention (CWC), which came into force in 1997, prohibits not only the use of chemical weapons but also their production, possession, and transfer. With the support of 188 states around the world, the CWC is one of the most widely adhered-to international treaties, and it has come to symbolize the idea that it is possible to "civilize" the conduct of war -- seemingly against all odds. The CWC marked the culmination of over a century of diplomacy condemning chemical weapons, and, as time has gone by, the use and even the possession of such weapons have become an international taboo. This tradition underpins Clinton's recent statement that the Assad regime's "behavior is reprehensible; their actions against their own people have been tragic," she continued, "But there is no doubt that there's a line between even the horrors that they've already inflicted on the Syrian people and moving to what would be an internationally condemned step of utilizing their chemical weapons."
Why are chemical weapons singled out as so intolerable? Observers have usually explained the taboo by speculating either that humans harbor a unique fear of poison or that militaries have never considered chemical weapons useful. But these theories do not stand up to scrutiny. From the crossbow to the firearm to the submarine, many new weapons technologies throughout history have been greeted with protestations that they cross the boundary of acceptable conduct even in war. Moreover, after World War I, the American Legion actually argued that poison gas was one of the most humane weapons of warfare, a preferable alternative to explosives and bayonets, which often left survivors maimed and suffering from horrifying infections. What galvanized the world's attention to try to ban these weapons after World War I was the fear that they could be employed with catastrophic lethality against civilian populations -- especially in future wars, in which air power might be used to devastate major cities.
That fact undercuts the assumption that militaries have avoided chemical weapons because they thought they could never be useful. The effort to head off their use began in earnest with the Hague Convention of 1899, which banned the use of projectiles that diffused "asphyxiating or deleterious gases." After witnessing the wide and devastating use of chemical weapons during World War I, diplomats agreed to the Geneva Protocol of 1925, which broadened the prohibition beyond projectiles to any "asphyxiating, poisonous or other gases." During World War II, neither the Allies nor the Germans unleashed chemical weapons on the front lines or in bombing campaigns against cities. (Both sides assessed that they were not adequately prepared to initiate chemical war, and they feared mutual retaliation.) Importantly, the warring parties were also constrained by norms and laws that were already setting chemical agents apart from other types of weapons. U.S. President Franklin Roosevelt, for example, was staunchly opposed to the use of gas in warfare. It was difficult for military leaders to win appropriations for a weapon that Washington had committed not to use first, despite some assessments regarding their potential battlefield utility. (U.S. General Alden H. Waitt maintained that "gas is the most promising of all weapons for overcoming cave defenses," which the Japanese used with such brutal effectiveness during the war in the Pacific.)
In other words, the taboo against chemical weapons is and always has been a distinctly moral and political limitation placed on war, requiring continual reinforcement. The fact that there has been an accumulated history of non-use -- whatever the reasons -- has itself come to constitute an important part of the sense that chemical weapons are taboo. The debates in the U.S. Congress over former Iraqi President Saddam Hussein's use of chemical weapons against Iran in the 1980s illustrate that point: it was remarked at the time that chemical weapons must be horrible, because even Hitler refused to use them against the Allies. Of course, no one participating in those debates knew the real reason why Nazi Germany did not unleash chemical weapons against Allied cities and soldiers on the fronts (and it is worth noting that the Nazis had no qualms about using poison gas to kill Jews and others during the Holocaust). But none of that mattered; at the time, the salient point was that chemical weapons must be especially egregious if even Hitler steered clear.
The Iran-Iraq War proved the resilience of the taboo. When Iraq first used chemical weapons against Iran in 1982 -- a desperate measure to try to turn the tide of a seemingly lost war -- the international reaction was muted. Emboldened, Saddam turned his chemical arsenal against the Kurds. It is noteworthy, however, that Saddam initiated Iraq's use of chemical weapons incrementally -- gradually moving from nonlethal tear gas to mustard gas, and only after repeated warnings -- indicating a keen appreciation for the possibility of international reaction. Further, even as Saddam proceeded to use chemical weapons, he refused to admit it; such behavior actually reinforced the notion that chemical weapons were politically sensitive.