On April 22, 1915, chlorine gas, wafted by favorable breezes, drifted from German lines toward enemy positions held by French troops near Ypres, Belgium. This was the first significant use of chemical weapons in a war in which 100,000 tons of chemical agents would be used by both sides to kill almost 30,000 soldiers and injure 500,000. The injured would include a German corporal whose voice, bearing traces of a gas attack, carried him, 15 years later, to Germany's pinnacle. The man who was U.S. president when Adolf Hitler committed suicide 30 Aprils after Germany's 1915 gas attack had been Capt. Harry Truman in 1918 when his artillery unit fired shells containing some of the chemical agents that the Allies had developed in response to what Germany did in 1915.

Such weapons, and especially mustard gas, which blistered skin and lungs, seemed so sinister that the 1925 Geneva Protocol banned their use in war, but not their development. This resulted in mutual deterrence during the next world war, during which poison gas was used only for genocide. Might this fact have motivated Israel's alleged attack on a Syrian air base a day and a half after the Syrian regime was again suspected of using a nerve agent against a rebel position in a Damascus suburb?

Since 1997, a chemical weapons convention joined by 192 nations, including Syria, has banned the production and use of such weapons, which illustrates the limits of arms-control agreements -- they control those who least need to be controlled. Denmark is impeccably compliant; Syria is not. Did anyone other than U.S. Secretary of State John Kerry believe his 2014 claim that "we got 100 percent" of Syria's chemical weapons removed from that country following the 2013 attack -- including the same Damascus suburb -- in which a nerve agent killed, according to the U.S. government, 426 children and 1,003 others.

U.S. ability to influence events in Syria has been vanishingly small since Barack Obama ignored the "red line" he drew in 2012 regarding Syrian chemical weapons. The "enormous consequences" Obama threatened turned out to be ... Kerry's chimerical accomplishment.

One year ago this month, Syria's regime used sarin, which prompted U.S. cruise missile attacks that did not deter last Saturday's use of chemical weapons. If at this late date the only, or primary, U.S. objective in Syria -- and it is not a contemptible one -- is to economize violence and minimize atrocities, the ghastly but optimal outcome is a swift final victory by Bashar Assad's regime. A negotiated end to this civil war has long been a fantasy: Negotiations did not end the American, Russian, Spanish or Chinese civil wars in 1865, 1920, 1939 and 1949, respectively.

Almost seven years have passed since Obama, a practitioner of ineffectual rightmindedness, announced in August 2011 that "the time has come for President Assad to step aside." Assad remains unconvinced of that and will rule the rubble. This question, however, remains: What, if anything, should the United States do in response to the gratuitous use -- it will not alter, or perhaps even hasten, the civil war's outcome -- of these odious and indiscriminate weapons in an urban setting?

America has embarked on an audacious, not-thought-through experiment. The nation is shrugging off its post-1945 leadership on behalf of democratic pluralism that makes nations lawful and tranquil, and is upending the world trading system it created. Saying goodbye to all that is saying hello to we know not what.

Contact George Will at georgewill@washpost.com.