Even among all the horrors of trench warfare and suicidal machine gun charges of World War I, the use of gas stood out. The Germans were the first to initiate gas warfare, launching a yellow-hued bath of chlorine gas towards the French lines at the battle of Ypres. The act was swiftly decried – and avenged with allied chemical warfare units. Though on the whole gas attacks accounted for a relatively small portion of war casualties, its use was banned by formal agreement at Geneva in the interwar years. Notably, the agreement omitted any reference to the development and stockpiling of such weapons – that would come six decades later.

On this day, January 11, in 1989 the Paris Conference on Chemical Weapons concluded, closing the loophole on stockpiling and reaffirming the main points of the Geneva Convention. The participating states, it said in a declaration “are determined to prevent any recourse to chemical weapons by completely eliminating them.”

The real need for the Paris Conference was less to destroy chemical weapon stores than to involve more third-world countries in the agreement, in addition to closing some more of the loopholes. For example, though chemicals created for the sole purpose of killing humans were banned in Geneva, certain herbicides were still allowed, giving the United States the legal basis for using Agent Orange in Vietnam.