Hague Declaration

The USA s refusal to adhere to the 1899 Hague Declaration meant that unanimity at the conference, a requirement of UK agreement, was impossible, and the UK did not so agree. In 1907, the UK did adhere to the declaration and became bound by it. France agreed with the 1899 Hague declaration, as did Germany, Italy, Russia and Japan. 

That the Germans had used it first and were considered by many to have violated the Hague Declarations. 

Carnegie Endowment for International Peace. 1915. The Hague Declaration (IV, 2) of 1899 Concerning Asphyxiating Gases,... 

February 1922. The Harding administration had several objectives in sponsoring the conference, principally naval disarmament, a disengagement of Britain from her pre-war alliance with Japan, and the resolution of outstanding Sino-Japanese disputes. Gas warfare was a comparatively minor issue, but the Harding administration still sought another international prohibition of poison gas to reaffirm international law, improve upon the Hague Declaration, and produce a statement which the American Senate could ratify (since it had failed to ratify the Treaty of Versailles). 

---