The shelling of suburban Damascus with a suspected nerve agent last week was potentially the third large-scale use of a chemical weapon in the Middle East and may have broken the longest period in history without such an attack.
If confirmed, the attack, which U.S. officials say warrants a decisive military response from the West, would dash hopes that the world would never again see the large-scale use of chemical weapons, a prospect that had appeared increasingly realistic in recent years as all but a handful of nations signed a treaty agreeing to destroy their stockpiles.
Chemical weapons attacks have at times elicited strong and visceral reactions from the international community.
During the Cold War, the United States and the Soviet Union raced to build enormous chemical weapons stockpiles. In 1969, President Richard Nixon, alarmed by the cost of America's chemical and biological weapons, announced that the United States would shut down its programs for both types of weapons, saying that their use was "repugnant to the conscience of mankind."
Both countries embarked on a costly and protracted effort to destroy their stockpiles. The undertaking gained steam as the United States ratified the Chemical Weapons Convention treaty in 1997 and vowed to get rid of its roughly 30,500 tons of munitions by 2012. Washington missed the deadline, but the Army remains committed to destroying the chemical weapons still securely stored at a handful of sites.
The only countries that have not signed the treaty are Angola, Egypt, North Korea, South Sudan and Syria. Israel has signed but not ratified it.