An unexploded mortar shell fired by the Syrian Army in the Mleha suburb of Damascus, January 25, 2013. (Goran Tomasevic / Courtesy Reuters)

The rebels in Syria could be excused for wondering what U.S. policy toward them might be. At times, President Barack Obama has implied that the United States can’t do much to help them because none of them has been gassed. By threatening “enormous consequences” should the Syrian regime use chemical weapons, he seemed to be saying that the first chemical attack would bring the Americans running in, guns blazing. Although understandable, that is likely to be a substantial misreading of the message coming out Washington.

The notion that killing with gas is more reprehensible than killing with bullets or shrapnel came out of World War I, in which chemical weapons, introduced by the Germans in 1915, were used extensively. The British emphasized the weapons’ inhumane aspects as part of their ongoing program to entice the United States into taking their side in the war. It is estimated that the British quintupled their gas casualty figures from the first German attack for dramatic effect.

As it happened, chemical weapons accounted for considerably less than one percent of the battle deaths in the war, and, on average, it took over a ton of gas to produce a single fatality. Only about two or three percent of those gassed on the Western front died. By contrast, wounds from a traditional weapon proved 10 to 12 times more likely to be fatal. After the war, some military analysts such as Basil Liddell Hart came to believe that chemical warfare was comparatively humane -- these weapons could incapacitate troops without killing many.

But that view lost out to the one that the British propagandists had put forward -- that chemical weapons were uniquely horrible and must, therefore, be banned. For the most part, the militaries of the combatant nations were quite happy to get rid of the weapons. As the official British history of the war concludes (in a footnote), gas "made war uncomfortable ... to no purpose."

To be sure, some armies occasionally still saw a purpose. Iraq made extensive use of chemical weapons in its 1980-88 war against Iran (to little outside protest). Their effectiveness in killing in that conflict remains a matter of some controversy. According to Iranian reports, of the 27,000 Iranians gassed through March 1987, only 262 died.

Other episodes in that war -- in particular, Baghdad’s chemical attack on the Iraqi Kurdish town of Halabja in 1988 -- have been held up as examples of the extensive destructive potential of chemical weapons. It is commonly contended that 5,000 people died as a result of the gas attacks. But the siege on the city took place over several days and involved explosive munitions as well. Moreover, journalists who were taken to the town shortly after the attack report that they saw at most “hundreds” of bodies. Although some of them report the 5,000 figure, this number is consistently identified as coming from Iranian authorities, an important qualification that was often lost in later accounts. The Iranians apparently also asserted that an additional 5,000 were wounded by the chemical weapons, even though experience suggests that any attack that killed 5,000 would have injured vastly more than that. Iraqi forces also used chemical weapons on other towns in the area. In two of these attacks, the most extreme reports maintain that 300 or 400 might have been killed. According to all other estimates, under 100 died. And most of those accounts figure that the death toll was under 20.

Back in the West, as the Cold War came to an end, the phrase “weapons of mass destruction” was coming into vogue. Earlier, the term had generally been taken as a dramatic synonym for nuclear weapons or weapons of similar destructive capacity that might be developed in the future. In 1992, however, the phrase was explicitly codified into American law and was determined to include not only nuclear weapons but chemical and biological ones as well. Then, in 1994, radiological weapons were added to the list. (The 1994 rendering also brought explosives into the mix. As a result, under this law almost all weapons apart from modern rifles and pistols are considered weapons of mass destruction: Revolutionary War muskets, Francis Scott Key’s bombs bursting in air, and potato guns would all qualify.)

A single nuclear weapon can indeed inflict massive destruction; a single chemical weapon cannot. For chemical weapons to cause extensive damage, many of them must be used -- just like conventional weapons. As a presidential advisory panel noted in 1999, it would take a full ton of sarin gas released under favorable weather conditions for the destructive effects to become distinctly greater than those that could be achieved with conventional explosives.

The muddling of the concept of weapons of mass destruction played a major role in the run-up to the 2003 war in Iraq. That campaign was mainly justified as a way to keep Saddam Hussein from obtaining uniquely destructive weapons. At least in the first instance, this meant chemical weapons, which Iraq had already shown itself capable of developing. Initial support for that war was impelled by the WMD confusion, and many analysts fear that alarm about chemical weapons could lead the United States into another disaster in Syria if they become the game changer that the Obama administration has proclaimed them to be.

Those fears are probably misplaced. The Iraq War, like the war in Afghanistan, was a response to 9/11. In the decade before those two wars, U.S. policy toward conflicts around the world had been primarily humanitarian. The United States did get involved sometimes, but rarely showed a willingness to sacrifice American lives in the process. Policy, then, was a combination of vast proclamation and half-vast execution. In Bosnia and Haiti, for example, intervention on the ground was held off until hostilities had ceased. Bombs, but no boots, were sent to Kosovo, and in Somalia the United States withdrew its troops as soon as 19 soldiers died in a firefight.

Although 9/11 disrupted that pattern, in its wake the United States has returned to limiting its involvement in conflicts around the world. Overall, we have not really witnessed the rise of a new militarism in the last couple of decades, as some analysts have suggested. The intervention in Libya was strained and hesitant, and Washington has showed little willingness to do much of anything about the conflict in neighboring Mali that was spawned by the Libyan venture. It seems unlikely, then, that chemical weapons in Syria -- however repugnant they may be taken to be -- will notably change that basic game.