Idealism and Institutions: The Interwar Evolution of International Relations

When the guns of the First World War finally fell silent in 1918, the world was left counting an unimaginable cost. Millions were dead, empires had collapsed, and an entire generation had been scarred by industrial-scale violence. Out of this devastation grew a powerful conviction: that war itself could be engineered out of existence through law, reason, and cooperation. The period between 1919 and 1945, often called the “Law and Organisation Stage” in the evolution of international relations, was the great experiment built on this hope. Statesmen and scholars believed that the right institutions and the right legal frameworks could tame the chaos of global politics. This is the story of that experiment, and of why its noble ambitions ultimately collapsed into a second world war.

The idealist foundation of the interwar order
Woodrow Wilson and the Fourteen Points
The League of Nations: idealism in concrete form
An early flaw in the foundation
Where the idealist experiment broke down
The Manchurian Crisis (1931)
The Abyssinian Crisis (1935-36)
The deeper structural weaknesses
The intellectual reckoning: Carr and the failure to build a theory
The legacy: lessons written into the United Nations

The idealist foundation of the interwar order

The intellectual engine of this stage was idealism, also called the institutional or normative approach. Idealists started from an optimistic view of human nature and international politics. They argued that war was not inevitable but was instead the product of misunderstanding, secret diplomacy, and the absence of a proper rule-based order. If those conditions could be fixed, peace would follow naturally.

This thinking did not appear from nowhere. Its philosophical roots stretch back to Enlightenment thinkers like Immanuel Kant and Jean-Jacques Rousseau, who imagined a world governed by reason, justice, and shared moral principles rather than by brute force. After 1919, these ideas moved from the realm of philosophy into the corridors of power.

The idealist programme rested on a few core commitments. The first was the creation of supranational institutions capable of harmonising and directing relations among nations. The second was the steady development of international law to outlaw war and, should war still occur, to limit its destructiveness. The third was a belief in open diplomacy and collective security as replacements for the old system of secret alliances and balance-of-power politics. As one survey of the period notes, idealists believed that by reforming and developing international law and organisation, it would be both possible and desirable to end the anarchy that had long defined relations among nations.

Woodrow Wilson and the Fourteen Points

No figure embodied this vision more than U.S. President Woodrow Wilson. His framework, often called the Wilsonian vision, gave the idealist movement its political language. Wilson championed principles such as national self-determination, the peaceful settlement of disputes, open covenants openly arrived at, and the establishment of a rule-based international order. The doctrine drew on the older belief, associated with thinkers like Mazzini, that there was no real conflict between nationalism and internationalism, and that each nation had a special contribution to make to the well-being of humanity. Wilson placed self-determination at the very heart of the 1919 peace settlement, hoping that free, self-governing nations would naturally cooperate rather than fight.

The League of Nations: idealism in concrete form

The idealist vision found its most ambitious expression in the League of Nations, established as part of the 1919 Treaty of Versailles. The League was the world’s first general-purpose international organisation dedicated to maintaining peace. Its purpose was to provide a permanent forum where nations could air grievances, negotiate solutions, and uphold international law instead of reaching for their weapons.

The mechanism at the heart of the League was collective security. The idea was elegant in theory: an act of aggression against any one member would be treated as an act of aggression against all members. The combined weight of the international community, expressed through diplomacy, economic sanctions, and if necessary military force, would deter any would-be aggressor. The League acted as an arbitrator, established commissions to investigate disputes, and could recommend sanctions to deter nations from engaging in war. Specialised agencies were also created to tackle issues like labour standards, health, and refugees, reflecting the belief that cooperation in practical matters would build trust over time.

An early flaw in the foundation

Ironically, the League was wounded from the very start by the absence of its own architect’s country. Although Woodrow Wilson was its driving force, the United States Senate refused to ratify the Treaty of Versailles, and so the United States never joined. This was an enormous blow. The most economically and militarily powerful nation in the world stood outside the institution meant to keep the global peace. The League came to be dominated instead by Britain and France, whose own colonial interests and national priorities would repeatedly compromise its decisions.

Where the idealist experiment broke down

For a few years in the 1920s, the system appeared to work. But the optimism rested on shaky ground. The fundamental problem was that idealism underestimated the realities of state interests and power dynamics. The approach assumed that states would subordinate their selfish national goals to the collective good. When that assumption was tested by serious crises in the 1930s, it shattered.

The Manchurian Crisis (1931)

The first major test came in East Asia. In 1931, Japan invaded the Chinese region of Manchuria and set up a puppet state called Manchukuo. China appealed directly to the League. The League responded exactly as its idealist design dictated: it set up a commission of inquiry, the Lytton Commission, to investigate. The trouble was that the commission took roughly eighteen months to deliver its findings, and during that entire time Japan simply continued its expansion. When the report finally concluded that Japan must withdraw, Japan’s response was to withdraw from the League itself in 1933. No meaningful sanctions were imposed, partly because Britain and France feared for their own colonial possessions in Asia. The League’s slow, deliberative machinery, designed for reasoned debate, proved hopelessly inadequate against a determined aggressor.

The Abyssinian Crisis (1935-36)

If Manchuria exposed the League’s weakness, the invasion of Abyssinia (modern Ethiopia) destroyed its credibility. In 1935, Mussolini’s Italy invaded Abyssinia. This time the League did impose economic sanctions, but they were deliberately weak and full of loopholes. Crucially, they did not include oil, the one commodity that might have crippled the Italian war machine, and the Suez Canal was kept open to Italian ships. Britain and France, more anxious to keep Italy as a potential ally against a rising Germany than to defend an African nation, even secretly negotiated to hand over much of Abyssinia to Italy. The episode revealed that Britain and France dominated the League and were willing to sacrifice the principle of collective security for their own strategic convenience.

The deeper structural weaknesses

These crises were symptoms of problems built into the system itself. Several weaknesses combined to doom the League:

No military force: The League had no standing army of its own. It depended entirely on member states being willing to contribute troops or enforce sanctions, and when their interests were not directly threatened, they declined to act.

Ineffective sanctions: Economic sanctions repeatedly failed because they relied on member compliance. Powerful aggressors often endured less hardship than the weaker economies that were supposed to enforce the penalties.

The Great Depression: The global economic crisis of 1929 to 1933 made matters far worse. Mass unemployment and financial ruin fuelled aggressive nationalism and made nations far less willing to bear the economic cost of defending others. This crisis at the level of the international system was a major cause of the breakdown of collective security.

A clash of national interests: The most fundamental contradiction was that specific national security interests proved irreconcilable with the abstract idea of security for all, by all. When push came to shove, states chose themselves.

The cumulative effect was disastrous. Each failure to act decisively, whether in Manchuria, Abyssinia, or later the Rhineland, sent a clear signal to aggressive powers that violations of international norms would go unpunished. This emboldened leaders like Hitler and Mussolini and helped clear the path to the Second World War.

The intellectual reckoning: Carr and the failure to build a theory

The collapse of the interwar order was not just a political failure; it was an intellectual one. This is one of the most important features of the Law and Organisation Stage. The era was so focused on building institutions and drafting legal codes that it failed to develop a genuine general theory of international relations. Scholars spent their energy describing how the world ought to be rather than analysing how it actually worked. They studied the structure of organisations and the text of treaties, but largely ignored the underlying forces of power, interest, and conflict that truly drive states.

This blind spot was exposed in 1939 by the British historian E. H. Carr in his landmark book The Twenty Years’ Crisis. Carr launched a devastating critique of what he called the utopianism of the interwar idealists. He argued that their optimistic outlook failed to account for the complexities and inherent conflicts of international politics. Against their faith in harmony, Carr insisted that international politics is fundamentally defined by power politics, identifying military power, economic power, and power over opinion as its central currencies.

Carr’s intervention is usually described as launching the so-called “first great debate” in IR, between idealism and the emerging school of realism. Yet it is worth noting that Carr was not a simple power-worshipper. He acknowledged that realism alone was insufficient, since pure realism offers nothing but a naked struggle for power that makes any international society impossible. He argued instead that sound political thought requires an uneasy balance between realism and idealism. But the damage to the idealist project was done. The realist critique demonstrated that you cannot wish power away simply by building institutions on top of it.

The legacy: lessons written into the United Nations

The Law and Organisation Stage ended in 1945 with the very catastrophe it had been designed to prevent. Yet its failure was not without value. When the victorious powers gathered to build a successor organisation, the United Nations, they consciously tried to fix the League’s flaws. The lessons of the interwar years were written directly into the new institution’s design.

The League’s most persistent vulnerabilities, including weak enforcement and the absence of major powers, directly shaped the structure of its successor. The UN created a powerful Security Council with permanent member status for the great powers, an attempt to ensure that the most important states stayed inside the system and were committed to enforcing its decisions. It also developed the concept of peacekeeping forces to give the organisation a more practical capacity to act. These design choices reflected an effort to address the League’s most persistent vulnerabilities while keeping the underlying goal of preventing another global war.

For the study of international relations as a discipline, the legacy is equally significant. The collapse of idealism cleared the ground for realism to dominate IR theory for decades to come, shifting the focus from praising or condemning state behaviour toward genuinely understanding its causes. The interwar period thus stands as a crucial first chapter in the discipline’s history, an ambitious experiment whose very failure taught later generations that any durable international order must be built on a clear-eyed reading of power, not on hope alone.

What do you think? Was the idealism of the interwar period a naive mistake, or was it a necessary first step that taught the world hard lessons it could not have learned any other way? And looking at international institutions today, have we truly solved the problem of enforcing collective security, or do the same weaknesses that doomed the League still linger beneath the surface?

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Table of Contents

The idealist foundation of the interwar order 🔗

Woodrow Wilson and the Fourteen Points 🔗

The League of Nations: idealism in concrete form 🔗

An early flaw in the foundation 🔗

Where the idealist experiment broke down 🔗

The Manchurian Crisis (1931) 🔗

The Abyssinian Crisis (1935-36) 🔗

The deeper structural weaknesses 🔗

The intellectual reckoning: Carr and the failure to build a theory 🔗

The legacy: lessons written into the United Nations 🔗