by Sakiko Kaiga
After the First World War of 1914–18, the League of Nations was established as the first experiment in an international organisation for peace. The League has often been remembered as a product of the yearning for peace, idealistic post-war views and the US President Woodrow Wilson’s leadership. Unlike the organisation’s image associated with idealism, the establishment of the League of Nations marked a shift towards ideological international politics. The beginning of the transition— from the nineteenth-century Concert of European Great Powers to the twentieth-century ideological battle—was already represented by the development of the pro-league of nations movement in Britain during the war.
The pro-league of nations movement was a non-governmental movement which, led by liberal intellectuals, promoted the idea of creating a new peaceful organisation to the public and politicians. Usually categorised as a peace movement, the pro-league movement and its thinkers have tended to be dismissed as utopians who could not understand how politics worked. As it has frequently been portrayed in previous studies, the pro-league of nations movement publicised a purely peaceful ideal and succeeded in obtaining the widespread support of the war-weary public in the later years of the war. However, most of the pro-league activists were neither pacifists nor opposed to the war, and their idea about the league defied the clear-cut categories of International Relations such as utopian or realist. In their theory, a basic premise of the creation of a league was the Allies’ victory. Pro-leaguers supported the on-going war and condemned war in general, which was hardly in conflict with their post-war project. Further, in their war prevention plan, realistic measures such as military sanctions and idealistic expectations on the moral force of public opinion were entwined as complementary ways. Both realistic and idealistic views, without excluding each other, developed their plan for peace which incorporated the collective use of force as a crucial element of the post-war order. Building on such views on future war prevention, the pro-league of nations movement aimed to devise a new system to maintain peace; the movement should therefore be better understood as a movement for international reform, rather than a peace movement. The idea about the league attracted leading statesmen such as British Foreign Secretary Edward Grey and was reflected by the official reports of the Phillimore Committee, the Foreign Office’s official study group on a league, which provided the basis for the discussion on the League of Nations Covenant at the Paris Peace Conference. Influencing decision-making as well as the development of international norms, the pro-league of nations movement played a role in the emergence of the new international order.
In fact, the contribution of the pro-league of nations movement to the new order was made by its unexpected, less straightforward, evolution during the war. The pro-league movement transformed its official idea about the post-war organisation into something unintended, by reflecting not the public’s craving for peace but the reality of people and nations at war. At the outbreak of the war in 1914 when the movement began, the pro-league of nations activists identified international anarchy and the rivalry of alliance blocs as the primary cause of war. They therefore sought to reform international relations by introducing a new international institution inclusive of all the great powers. Yet, by the end of the conflict in 1918, the pro-leaguers came to promote what they had originally opposed: the league as a continuation of the war-time alliance against Germany and its allies into the post-war peace. Behind this profound shift lay a powerful argument to fight until Germany was defeated, and a widely-shared belief that a new international organisation for peace should be formed as a coalition only of ‘democratic’ states. We will see why and how this shift unfolded, by tracing the ideas of the leading members of the pro-league movement, especially those of the Bryce Group, one of the first pro-league circles in Britain, and its successor, the League of Nations Society. It reveals how post-war ideas were elaborated inside the movement and publicly promoted in Britain from 1914 to 1919—a crucial period that framed the power and limitations of the League of Nations.
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In the course of its development, the pro-league of nations movement and its post-war ideas needed to be in tandem with the war. The more popular and influential the pro-league movement became, the less control the original leadership enjoyed over its direction. In 1915, the Bryce Group’s Proposals for the Avoidance of War, the first scheme of an international organisation during the war, provided the springboard for the subsequent debate about a new world order. Inspired by the Proposals, the League of Nations Society campaigned for the foundation of a post-war organisation, but in 1915–16 worked undercover to avoid being denounced as a pacifist movement. Finally in May 1917, the Society held its first public meeting and the idea of a league obtained widespread public support. Thus, the League of Nations Society made great strides in making its case popular and legitimate, yet at the same time began to lose control of the debate about what the league would look like. In popularising their ideas, the pro-leaguers underscored only the establishment of a new organisation without going into details, and lost the nuance and sophistication of their original proposal.
Simplifying the message for mass consumption was both a strength and a limitation. The activists lost control of the league project, by abandoning in-depth discussions about the post-war plan; yet, it also enabled the idea to be interpreted widely and to develop politically, which helped fulfil the ultimate goal of the pro-leaguers—the foundation of a new organisation. By the end of the First World War, its unprecedented scale and casualties compelled governments to justify the fight by a higher cause beyond national defence or interests. For this purpose, the war was framed as an ideological struggle for a peaceful international order, which paradoxically served to intensify the violence and also to legitimise the continuation of the war until victory. Under such circumstances, the only way the idea of a league of nations could become a popular, legitimate, and practical political project in Britain was if it was consistent with the defeat of Germany and its allies. The idea of a league was upheld as a war aim, part of the moral crusade of the western powers against German barbarism. Even though the pro-leaguers hoped for a new peaceful organisation and fought for a higher cause such as ‘a war against war’, in reality they fought for victory over enemy states. Fighting against states entailed seeking military victory as well as political and ideological supremacy, and that required the mobilisation of the public and their hatred of the enemy. The truth that war involved hate and violence was an essential problem that pro-league activists had to acknowledge for their purpose of achieving a new world order.
Indeed, the long, horrible, experience of the First World War neither transformed the public attitude into opposition to war in and of itself nor accelerated the development of the idea about the league of nations. Instead, the war led people to require legitimate and ideological reasons for going to war in the future. Prior to 1914, the reasons for going to war could be varied—conquest, defence, and sometimes honour. Fuelled by jingoism and war’s image as something short, heroic and rewarding, the public was not particularly inclined to consider whether there were ‘righteous’ reasons for waging war. In the case of Britain but also elsewhere, the First World War recast the way in which popular support for mass participation in war would be mobilised, and war for the preservation of peace became the most legitimate cause. The British public supported the creation of an international organisation to prevent war, not simply because of war-weariness or a longing for peace, but because of their recognition that the League would be a democratic alliance of peace-loving nations against German militarism. From the First World War to the Cold War, what constituted the legitimate use of military force was transformed, and the concept of peace itself became the focal point for intensifying ideological antagonism in the international spheres.
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By the establishment of the League of Nations, liberal values such as disarmament and international cooperation took centre stage in the international arena for the first time. Simultaneously, it highlighted the limits of liberal internationalism—a recently challenged and re-examined concept. Although the League of Nations was originally intended as an institution for war prevention and peaceful conflict resolution, it was not designed to prevent all wars but only certain types of war. Collective security that was introduced in the League ultimately hinged upon the use of force, military sanctions, as the last yet valid and indispensable measure for the maintenance of peace. Already in the early years of the war, the possibility of triggering or escalating war by relying on the use of force as a final resort was intensely debated by the pro-league thinkers. They nonetheless ended up envisaging an organisation which they simply anticipated would evolve over time, however imperfect the original form had been. They assumed military sanctions would be replaced in the future by a viable alternative—the force of public opinion—that would underpin a peaceful, stable international society. Founded upon liberal internationalists’ belief about progress, many British pro-leaguers anticipated public opinion would gradually develop and become a strong measure to prevent war. Although educating public opinion would need time and collective force would initially be required, the league would, once international morality was developed, evolve into the organisation that relied upon the force of public opinion. Supposing the threat of collective action would be less and less crucial in the future war prevention mechanism, pro-league thinkers left a question how such a vision of the league could be realised after the war and in the next generations. By looking at the emerging period of liberal internationalism, we can uncover the origin of its fundamental conundrum—the maintenance of world peace critically depends on the use of force—an issue that is still unsolved to this day.
 Henry R. Winkler, The League of Nations Movement in Great Britain 1914-1919 (Rutgers University Press, 1952); George W. Egerton, Great Britain and the Creation of the League of Nations: Strategy, Politics, and International Organization, 1914 -1919 (Scolar Press, 1978); Tony Smith, Why Wilson Matters: The Origin of American Liberal Internationalism and Its Crisis Today (Princeton University Press, 2017); Thomas J. Knock, To End All Wars: Woodrow Wilson and the Quest for a New World Order (Oxford University Press, 1992).
 Keith Robbins, The Abolition of War: the ’Peace Movement’ in Britain, 1914-1919 (University of Wales Press, 1976); Winkler, The League of Nations Movement in Great Britain.
 E. H. Carr, The Twenty Years’ Crisis, 1919-1939: An Introduction to the Study of International Relations (Macmillan, 2001), pp. 97-8.
 For example, Peter J. Yearwood, Guarantee of Peace: the League of Nations in British Policy, 1914-1925 (Oxford University Press, 2009).
 For more details, see Chapter Two in Sakiko Kaiga, Britain and the Intellectual Origins of the League of Nations, 1914-1919 (Cambridge University Press, 2021).
 William Mulligan, The Great War for Peace (Yale University Press, 2014), p. 10; Paul W. Schroeder, Systems, Stability, and Statecraft: Essays on the International History of Modern Europe (Palgrave Macmillan, 2004), pp. 249, 258, 263-4.
 The League of Nations Society’s strategies to garner popular support are discussed in Chapter Three in Kaiga, Britain and the Intellectual Origins of the League of Nations.
 For example in Britain, Philip Kerr, a private secretary of the Prime Minister and a leader of the Round Table, envisaged a league that could strengthen the unity of the British Empire and promote Anglo-American harmony.
 Mulligan, The Great War for Peace, pp. 7-9.
 Ibid., pp. 8-9.
 I. F. Clarke, Voices Prophesying War, 1763-1984 (Oxford University Press, 1966), pp. 131, 162.
 The relationship between two pro-league groups in Britain and the US, the League of Nations Society and the League to Enforce Peace, is examined in Kaiga, Britain and the Intellectual Origins of the League of Nations, Chapter Four. Even though the two groups had a lot in common and worked for the same goal of reforming the global order, they could not establish a constructive collaboration because of the differences in their domestic contexts and in the British and American liberal internationalist traditions. The chapter focuses only on pro-leaguers in Britain and America because ‘[t]he English showed much more interest in an international organization than did advocates elsewhere in Europe, and their ideas must be compared with those in the US’, as Kuehl has pointed out in Warren Kuehl, Seeking World Order: The United States and International Organization to 1920 (Vanderbilt University Press, 1969), p. 236. Further, in France, the discussion about the league was intensified only after American entry into the war in 1917, and the French pro-league work was mostly led by the government, not by private groups as in Britain and the US.
 For example, see ‘Ordering the World? Liberal Internationalism in Theory and Practice’, International Affairs, Vol. 94, Issue 1, (January 2018); ‘Rising Powers and the International Order’, Ethics & International Affairs, Vol. 32, issue 1 (Spring 2018); ‘Out of Order? The Future of the International System’, Foreign Affairs, Vol. 96, Number 1 (January/February 2017); ‘Is Democracy Dying? Global Report’, Foreign Affairs, Vol 97, Number 3 (May/June 2018).
 While the British liberal internationalists expected gradual progress in international society, the American counterparts called for a dramatic and swift change of the world system. Believing in progressive history and radical development after the war, American activists supposed a league should be organised as a single community with law and a police force. For more details, see Kaiga, Britain and the Intellectual Origins of the League of Nations, Chapter Four.