The 1925 Geneva Protocol: The League of Nations’ Only Arms Control Agreement
Historical Notes #6 (July 2025), 107pp.
The origins of the Geneva Protocol and the history of its negotiation 100 years ago, including an analysis of why Poland insisted on inserting bacteriological weapons in the document.
For download.
On Wednesday, 17 June 1925, the Conference for the Supervision of the International Traffic in Arms successfully concluded six weeks of negotiations with three agreements. One of them was the Protocol for the Prohibition of the Use in War of Asphyxiating, Poisonous or Other Gases, and of Bacteriological Methods of Warfare. Of the forty-four participating delegations, twenty-six possessed plenipotentiary power to sign the Protocol before the closing of the Conference. Another twelve states affixed their signatures and ratified the document before its general entry into force on 8 February 1928. As of June 2025, 147 states are party to the Geneva Protocol, as the legal instrument is commonly known.
Despite being a mere single-page long, the agreement has limited the use of chemical weapons (CW) in armed conflicts and all but prevented the deliberate spread of disease as a method of warfare. Being part of the laws of war, it did not forbid the development, production and possession of chemical and bacteriological (biological) weapons (CBW). Still, it paved the way for the 1972 Biological and Toxin Weapons Convention (BTWC) and the 1993 Chemical Weapons Convention (CWC). In addition, it provides the legal foundation for the UN Secretary-General’s Mechanism to investigate alleged CBW use. The 1998 Rome Statute, which established the International Criminal Court, uses Protocol language to declare CW use a war crime. (A later amendment added BW use to the list of war crimes but utilised the reference to biological and bacteriological agents in the BTWC.)
While today nobody contests the Geneva Protocol’s contribution to the development of the norm against CBW, little is known about the factors that contributed to its emergence and negotiation. Why was the document a protocol and not a treaty? Given the supposed widespread abhorrence against CW after the massive and systematic use of gas during the First World War, why did it take almost seven years for the international community to translate this repugnance into a global ban? Why did the centuries-old customary prohibition of poison use, codified for the first time at the 1899 Hague Convention and restated at the 1907 Hague Convention, no longer suffice? How did the negotiators, seemingly out of nowhere, decide to include disease as a method of warfare in the Protocol? This issue of Historical Studies aims to answer these and many other questions.
The Geneva Protocol and its antecedents
Chapter 1 traces the evolution of the norm against the use of poison and poisoned weapons from Antiquity through the Middle Ages and the Early Modern Times to their codification in international law in 1899. However, the 1899 Hague Peace Conference yielded a second document addressing the use of poisonous substances in war, the Declaration (IV, 2). The latter accord used the different but related terminology of ‘asphyxiating’ and ‘deleterious’ gases. It pointed to a semantic bifurcation that unfolded through the 1800s. ‘Poison’ became associated with the naturally occurring toxic substances, whereas the newer terms referred to human-made toxicants. The harmful exposure of factory workers, the public and the environment to these substances gave rise to specific national legislation and international treaties in the 19th century. The proposal to ban the new toxicants from the battlefield had its roots in those regulations. Still, not everybody was convinced that these industrial chemical compounds would be less humane than other modes of warfare, more so as nobody had yet used them as a weapon. The refusal of two participating states to sign the Declaration confirmed the semantic split. From then on, poisons and asphyxiating or deleterious gases would follow their separate trajectories of prohibition, the latter leading to the Geneva Protocol.
The Treaty of Versailles and the disarmament of Germany
The second chapter discusses the crafting of the 1919 Treaty of Versailles, which established the League of Nations and contained the peace arrangements with Germany. The League was eventually the institution under whose auspices the Geneva Protocol would be negotiated. However, nothing in the Covenant indicated that the regulation of warfare was a topic in which the international organisation could be involved. The League’s ultimate aim was the elimination of war, not a particular type of warfare. In stark contrast to the League’s lofty ambitions, the victors imposed a coercive disarmament regime on Germany. The strict conditions had multiple consequences, both for the German population and the Allies. In Germany, the so-called war guilt clause and the punitive reparations caused a lot of resentment. In the victorious countries, the spoils of war did not meet the expectations that governments had promised to recompense for the suffering caused by harsh war conditions. Moreover, President Woodrow Wilson disagreed fundamentally with the European demands, a significant factor in the US decision not to ratify the Treaty of Versailles and negotiate a separate peace treaty with Germany. The League tried to fulfil its primary objective by seeking the lowest levels of national armaments and developing an arbitration system to resolve any disputes among its members. It also sought to establish a collective security system based on mutual assistance. For France, a neighbour of Germany, the latter setup was a fundamental prerequisite without which it refused to contemplate any reduction in armaments or military personnel. Great Britain and the United States baulked at transferring their sovereign authority on declaring war to an international body.
Early consideration of asphyxiating gases and bacteriological agents
Chapter 3 describes how the issue of chemical warfare was introduced into the discussions in the League of Nations committees. It first examines Germany’s prohibition on possessing, developing, producing, or importing CW as outlined in the Treaty of Versailles. The paragraphs in Articles 171 and 172 drew on the language in the Hague Declaration (IV, 2). They also contained the first legal explication of a CW, which comprised three parts and, as such, formed the forerunner of the definitions of a BW and CW in the BTWC and CWC. A couple of years later, many delegates came to regard the proscription as applying to other League members as well, which would influence the nature of CW-related discussions.
Meanwhile, the structure of the League of Nations and its principle of transparent decision-making were to play an important role. None of the former belligerents felt rushed to eliminate chemical warfare, and they continued their CW programmes. While the League Council ensured the interests of the major powers, the Assembly represented all League members on an equal footing. Moreover, the Assembly allowed delegates to raise matters of great urgency or public interest. Thus, chemical warfare entered the debates, and the responses given by the Council would provide clues on how to rephrase the CW problem so that it became more aligned with the League’s core activities. A primary line of resistance to addressing CW was that the League was not in the business of developing new war regulations.
At the end of 1921, the United States convened the Washington Naval Conference to seek arms reductions among the five major powers: France, Great Britain, Italy, Japan and the United States. One of the committees on novel modes of warfare addressed asphyxiating or deleterious substances. All five delegations signed the resulting treaty, which addressed both submarine warfare and noxious gases, early in February 1922, and all except France ratified it. The agreement also promised that upon its entry into force, the United States, as the depositary state, would invite all other states to accede to it. The document, whose Article V contained the language that was to form the core of the Geneva Protocol, would dramatically change the nature of the CW debates in the League. Not only had the great powers committed themselves to a new rule of warfare, which meant that the League did not have to negotiate it, but the promise of universalisation also galvanised the Assembly to ensure that all League members would adhere to it once the US invitation arrived.
Understanding future threats from chemical and bacteriological warfare
Because France refused to ratify the Washington Treaty due to its disagreement with the provisions on submarine warfare, the US invitation never arrived. As analysed in Chapter 4, this did not deter the proponents of abolishing chemical warfare in the Assembly. When more studies on future warfare came out and people began appreciating the implications of future (aerial) warfare with toxic chemicals for civilian populations, the new debates offered opportunities to reframe the CW question as one of technological development and armament that were contrary to the core objectives of the League of Nations. The committee on noxious gases in Washington reinforced those sentiments. It had concluded that it was impossible to regulate chemical warfare or CW production because most toxic compounds had essential industrial or commercial applications. Accordingly, it proposed to legalise chemical warfare against military land and naval targets and limit the restriction to civilian population centres only, all the while recognising that discrimination between combatants and non-combatants would not always be possible. US intervention blocked those recommendations, and the Conference adopted an alternative resolution that became Article V of the Washington Treaty.
With future threat scenarios in mind, the Assembly requested a study into the prospect of future chemical warfare agents. Meanwhile, the question of bacteriological warfare had also entered the debates, so the analysis was to include those possibilities as well. It contained the assessments and recommendations of invited chemists and bacteriologists. In 1924, the League approved the report and recommended that League members publish and distribute it to their population. No further action was undertaken.
That year, the first phase of the League came to an end. The immediate future foresaw the negotiation of an arms trade convention under the League’s auspices in the spring of 1925, as well as preparations for a treaty regulating the armaments industry and, in a more distant future, a general disarmament treaty.
Negotiation of the Geneva Protocol
The Conference for the Supervision of the International Trade in Arms and Ammunition and in Implements of War began on 4 May 1925. Six weeks later, on 17 June, diplomats lined up to sign not just the Arms Traffic Convention but also the Geneva Protocol. Chapter 5 describes how US and Polish amendments to add CW and BW to the proposed regulation of the international arms trade, one of the League’s core tasks, eventually led to the negotiation of a separate agreement outlawing chemical and bacteriological warfare. The process was complicated because delegates had to confront several profound questions, not all of which they were able to resolve. Due to the Conference’s focus on weapons and munitions rather than on the humanitarian consequences of their use on the battlefield, the delegates had to engage with the international legal status and technical properties of CBW. The core of the debates centred on CW; the nature of the Polish amendment meant that any agreement on CW would apply mutatis mutandis to BW. At the Washington Conference, diplomats had already encountered the dual-use nature of toxic chemicals and decided that, therefore, they could not prohibit the production of poisonous agents. It was one of the reasons why the committee on noxious gases suggested legalising chemical warfare. To regulate the international transfer of toxicants, the Geneva meeting had to come up with an approach to differentiate between legitimate poisonous substances and those used in warfare. It drew extensively on the scientific assessments by the chemists and the bacteriologists consulted by the League in 1923 and 1924. The task proved impossible because the chemical compounds were the same.
A legal corollary of the dual-use question was whether it was possible to regulate the international trade in toxic chemicals without an international legal regime banning chemical warfare. The delegates concluded that despite the Treaty of Versailles and the Washington Treaty, which had not yet entered into force, there was no such global ban.
A third serious matter concerned the security implications of the proposed trade prohibition for smaller states with limited industrial capacities. They potentially faced a situation in which nations with a large and advanced chemical industry could manufacture CW without any limitations. At the same time, the proposed trade restrictions would deny smaller nations the ability to acquire a retaliatory capacity unless they initiated CW production themselves. The latter suggestion went against the League’s core objective of armament reductions and the limitation of arms production.
Due to these questions, the US CW proposal became detached from consideration of the Arms Traffic Convention, and it evolved into a separate document derived from Article V of the Washington Treaty. In the final stages of the Arms Traffic Conference, Poland reminded the participating states of its proposal to add bacteriological warfare to any agreement on CW in an impassioned speech. No delegate objected.
Poland and the consideration of bacteriological methods of warfare
The sixth chapter delves deeper into how bacteriological methods of warfare became an international security concern on a par with chemical warfare and why exactly Poland was such an ardent proponent of its inclusion in any instrument regulating CW. Different factors played a role. During the First World War, several acts of sabotage involving cultivated bacteria occurred. While most incidents remained unknown at the time, the discovery of several vials with pathogens in the German legation in Bucharest was widely publicised.
During the First World War and the wars with Russia, Poland suffered several pandemics – typhus, cholera and the so-called Spanish influenza – killing hundreds of thousands of people and leaving the future independent state destitute. The head of the Polish delegation in Geneva, General Kazimierz Sosnkowski, played a central role in the Arms Traffic Conference. As a person firmly committed to Polish independence, he had led several military campaigns against Russian Imperial and Bolshevik forces amid the outbreaks of disease. The so-called Spanish influenza touched him personally. When Poland achieved independence after the First World War and gained international recognition through its membership in the League of Nations, the country was aware of its precarious security condition, sharing long borders with Germany to the west and Russia to the east. It therefore sought maximal mutual security assurances. Unlike Germany, Bolshevik Russia did not participate in the Arms Traffic Conference and would hence not be bound by any agreement emerging from the Geneva Conference.
In 1924 and 1925, rumours in the international press, whether true or not, suggested that Russia had embarked on an offensive BW programme. So, when a technical amendment to include CW in the deliberations evolved into a separate international agreement laying out an overall restriction on chemical warfare, Poland insisted on the inclusion of pathogens as an emerging weapon in the Protocol as part of an overarching international security guarantee against a threat from its eastern neighbour.
The legacy of the 1925 Geneva Protocol
The concluding chapter reflects on the contributions of the Geneva Protocol, the only significant achievement in weapon control by the League of Nations, to international security and disarmament, particularly to the BTWC and CWC, as well as other international instruments that draw on its ban on chemical and biological warfare.
Jean Pascal Zanders, The 1925 Geneva Protocol: The League of Nations’ Only Arms Control Agreement, Historical Notes #6 (The Trench), July 2025, 107pp. For download.
