What treaty outlawed biological warfare?

The Geneva Protocol of 1925 specifically addresses the prohibition of "asphyxiating, poisonous or other gases, and of bacteriological methods of warfare." This treaty was pivotal in the efforts to restrict the use of chemical and biological weapons in conflicts, reflecting the global consensus against the horrors of such warfare, particularly following the experiences of World War I. The protocol built upon the principles established in earlier conventions, but it is significant for its explicit mention of biological warfare, making it a cornerstone document in the efforts to regulate and ultimately outlaw this form of combat.

While the Geneva Convention focuses broadly on humanitarian treatment during wartime and the protection of individuals, it does not specifically single out biological warfare in the way the Geneva Protocol does. The Treaty of Versailles was primarily concerned with establishing peace after World War I and imposing reparations on Germany, without direct references to biological weapons. The Hague Conventions dealt with various aspects of the laws of war but did not specifically outlaw biological warfare either. Therefore, the Geneva Protocol of 1925 is the most relevant treaty when discussing the outlawing of biological warfare.