Using biological and chemical weapons was condemned by international declarations and treaties, notably by the 1907 Hague Convention (IV) respecting the laws and customs of war on land. Efforts to strengthen this prohibition resulted in the conclusion, in 1925, of the Geneva Protocol, which banned the use of asphyxiating, poisonous or other gases, usually referred to as chemical weapons, as well as the use of bacteriological methods of warfare. The latter are now understood to include not only bacteria, but also other biological agents, such as viruses or rickettsiae which were unknown at the time the Geneva Protocol was signed. However, the Geneva Protocol did not prohibit the development, production and stockpiling of chemical and biological weapons. Attempts to achieve a complete ban were made in the 1930s in the framework of the League of Nations, but with no success.