AUDIE CORNISH, HOST:
When President Obama addressed the question of Syria in his news conference yesterday, he said the use of chemical weapons violates important international norms.
SOUNDBITE OF NEWS CONFERENCE
PRESIDENT BARACK OBAMA: ...That say, when you use these kinds of weapons, you have the potential of killing massive numbers of people in the most inhumane way possible; and the proliferation risks are so significant that we don't want that genie out of the bottle.
CORNISH: But why this focus on the use of chemical weapons when conventional weapons have already killed tens of thousands in Syria? As NPR's Larry Abramson reports, the answer goes back to the early uses of poison gas nearly a century ago.
LARRY ABRAMSON, BYLINE: In World War I, trench warfare led to stalemates, and to new weapons meant to break through the lines.
(SOUNDBITE OF MOVIE, "ALL QUIET ON THE WESTERN FRONT")
UNIDENTIFIED ACTOR #1: (As character) Gas masks!
UNIDENTIFIED ACTOR #2: (As character) Gas, the most feared, the most obscene weapon of all. We remember the awful sights in the hospital, the gas patients.
ABRAMSON: This remake of "All Quiet on the Western Front" recalls some of the horror associated with gas in World War I. Gas only caused a small percentage of the war deaths. But as Greg Thielman, of the Arms Control Association, notes, it left behind a frightening legacy in the form of a million survivors.
GREG THIELMAN: Which meant painful lung diseases, a lot of people blind for the rest of their lives. That meant, for example, in America there were tens of thousands of people who were scarred by exposure to mustard agent in World War I.
ABRAMSON: Reaction to those deaths and injuries was swift. By 1925, the League of Nations had approved the Geneva Protocol, which banned the use of chemical weapons. In World War II, their use was extremely limited. Adolf Hitler, himself a victim of gas in the First World War, never used his stockpiles on the battlefield.
But during the Cold War, the U.S. and the Soviet Union produced massive quantities of chemical and biological weapons. The end of the Soviet Union paved the way to an historic step - the 1993 treaty that banned the production, stockpiling and use of these weapons.
Michael Luhan is spokesman for the Organization for the Prohibition of Chemical Weapons, which oversees enforcement of that treaty.
MICHAEL LUHAN: Sixteen years on, we have now verified the destruction of about 80 percent of all the chemical weapon stockpiles that have been declared to us.
ABRAMSON: But obviously, that success has not removed chemical weapons from the list of global threats. A century after their first use, these weapons still have the power to terrify, in part because civilian populations are so vulnerable.
Greg Thielman, who worked in the State Department for decades, points out that militaries have learned how to shield their troops with protective gear.
THIELMAN: And what that meant was that the main victims of chemical weapons in modern war are those who are not so equipped, which means mostly civilians.
ABRAMSON: Daryl Kimball, of the Arms Control Association says the use of chemical weapons in Syria could constitute a war crime, especially if used deliberately against civilians. He says Syrian commanders on the ground should take note.
DARYL KIMBALL: Those that do not cooperate in any orders to use these weapons, they will be treated much more leniently and, you know, their actions will be taken into account in the post-war situation.
ABRAMSON: Kimball concedes international prosecution of such a crime would be difficult. And at this point, Bashar al-Assad and his commanders may feel they have little left to lose.
Larry Abramson, NPR News, Washington.