The Geneva Protocol

Using language from the unsuccessful 1921–22 Washington Naval Conference and referring to previously agreed provisions of the 1899 Hague Declaration and the 1919 Treaty of Versailles, member states finally agreed to prohibit the use of chemical weapons in war. The Geneva Protocol states,

Whereas the use in war of asphyxiating, poisonous or other gases, and of all analogous liquids materials of devices, has been justly condemned by the general opinion of the civilized world; and

Whereas the prohibition of such use has been declared in Treaties to which the majority of Powers of the world are Parties; and

To the end that this prohibition shall be universally accepted as a part of International Law, binding alike the conscience and the practice of nations;

Declare:

That the High Contracting Parties, so far as they are not already Parties to Treaties prohibiting such use, accept this prohibition, agree to extend this prohibition to the use of bacteriological methods of warfare and agree to be bound as between themselves according to the terms of this declaration.

http://www.icrc.org/ihl.nsf/FULL/280?OpenDocument

With this agreement, many believed the Geneva Protocol was the beginning of the end of chemical weapons. However, immediately following the conference chemical warfare advocates began a concerted campaign to keep the United States Senate from ratifying the treaty.