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.