Classical Liberalism in International Relations

In International Relations, classical liberalism explains war and cooperation by asking how the internal character of states changes their behavior abroad. It begins from a problem shared by many international relations theories: states operate without a world government able to command them all. Realists usually stress what this condition does between states. Classical liberals add a domestic question: before a state fights, what domestic path must the decision pass through? When war has to be defended before taxpayers and representative institutions, force becomes harder to treat as personal policy.

Classical liberalism is therefore optimistic only in a qualified sense. This tradition grew out of a suspicion of concentrated power, and that suspicion applies to international politics as much as to domestic government. In foreign policy, the danger is concrete: war can give rulers an emergency argument for demanding new revenue, claiming wider executive powers and treating opposition as a threat to security. Protectionism and empire create a similar risk when governments use external policy to favor protected groups. For that reason, classical liberalism treats peace as a political achievement: it depends on rules and social conditions that make coercion harder to authorize and less profitable to pursue.

The label can be confusing because liberalism in IR later became a broader family of theories. Democratic peace theory develops the republican claim that accountable governments are less likely to fight one another. Commercial liberalism asks how trade and interdependence change the payoff of conquest. Liberal institutionalism studies how rules and organizations make promises easier to monitor. Classical liberalism is narrower than this later family: it begins with limited government and individual rights, then asks how open exchange and legal restraint alter foreign policy and international order.

Summary

• In IR, classical liberalism argues that international politics depends on more than military power or the balance among states. Domestic institutions shape what governments want, which groups influence policy and how easily leaders can shift the costs of conflict onto society.
• Republican government can make war politically harder because citizens bear its costs. Voters can punish leaders, legislatures can scrutinize spending, and public debate can force governments to justify why violence is necessary.
• Commerce changes the value of conquest. When prosperity depends on exchange under general rules, occupying territory may damage the financial trust and production networks that made that territory valuable.
• Public rules and recurring forums can make commitments easier to monitor and violations harder to hide. They cannot abolish power politics, but they can give states a shared language for protest, justification and bargaining.
• The strongest classical liberal claim is conditional: peace becomes more likely when domestic and international arrangements reward restraint more than coercion.

Origins and Precursors of Classical Liberalism

Classical liberalism emerged from early modern and Enlightenment arguments against arbitrary rule. In domestic politics, liberal writers challenged the idea that rulers could treat people, property claims and legal rules as extensions of personal authority. They defended consent and legal equality, and they argued that executives could not tax property, police conscience or bypass representation as if society belonged to them. When those ideas entered international thought, they changed the question of war. If government exists to protect rights, foreign policy cannot be treated as a private instrument of kings, ministers or military elites. War now required political justification.

John Locke helped build this background by tying legitimate government to consent and the protection of life, liberty and property. His contribution to IR works through the domestic foundation of the theory. Locke left no full theory of world politics, yet his account of limited authority implies that the internal character of the state affects how it may use force abroad. In IR, Locke’s relevance lies in the idea that legitimate power is limited power, so taxation, conscription and war require stronger justification than they would under personal rule.

Montesquieu and Adam Smith contributed the commercial side of the argument. For Montesquieu, commerce did more than move goods. Repeated exchange taught people to weigh the cost of conflict, keep regular contact with foreigners and rely on predictable rules for payment and delivery. Smith then explained how specialization could create social wealth without a central authority directing every transaction. Applied internationally, these arguments suggested that foreigners could appear as partners in prosperity, rather than simply as enemies or rivals.

Beyond political economy, earlier legal and peace projects also shaped classical liberalism. Hugo Grotius helped later liberals argue that war could be judged by legal rules rather than only by victory, while proposals for federations or congresses of states imagined regular procedures for disputes. These ideas left sovereignty in place, but they tried to discipline sovereign power by making war answerable to public rules and recurring negotiation. The tension between sovereign independence and legal restraint became one of classical liberalism’s recurring problems.

Core Assumptions of Classical Liberalism

In IR, the core assumptions of classical liberalism explain why the theory looks inside the state before treating foreign policy as a single national will. They do not deny that states face external threats. Instead, they ask how rights, interests and institutions shape the way a state defines those threats and chooses a response.

First, individuals and social groups help form state preferences. Classical liberals treat the state as an arena in which social interests become public policy. A single war illustrates the point: military officials may describe it as necessary for security, merchants may experience it as a commercial loss, taxpayers may see it as a new burden, and bureaucracies may gain authority from managing it. The state acts internationally, but the preferences that guide state action are formed through domestic society and political institutions.

Second, anarchy exerts pressure without erasing political difference. In realism, the absence of a world government pushes states toward self-help, suspicion and competition. Classical liberalism accepts that anarchy creates danger, but it treats external pressure as only part of the explanation. A constitutional republic and an imperial bureaucracy can face a similar threat while producing different policies because they represent different domestic interests and face different restraints.

Third, cooperation can produce absolute gains. States may compete over relative advantage, especially in security affairs, but many problems allow more than one side to benefit. Navigation rules, public-health cooperation and arms-control agreements, for instance, can create gains that would be lost through conflict. For classical liberals, the possibility of mutual benefit gives politics something to organize: institutions and rules can make cooperation credible enough for states to choose it.

Fourth, the theory is suspicious of concentrated authority even when that authority promises order. A world government strong enough to enforce peace might also become a global despotism. Many liberal peace proposals therefore avoid unlimited supranational command. Some rely on federations or arbitration to regularize bargaining among independent states. Others rely on publicity and constitutional limits to make decisions for war visible at home. The point is to restrain violence without creating a more dangerous concentration of power.

Main Arguments of Classical Liberalism

The main arguments of classical liberalism turn those assumptions into mechanisms. They answer the same question from different angles: what makes war easier or harder for governments to choose? Representative accountability changes who must authorize war and bear its costs. Open commerce changes what conquest is worth. Public rules and recurring forums change how governments state claims, monitor promises and manage disputes. These emphases often overlap because authors can combine domestic, economic and legal restraint in the same account of peace.

One route to peace begins with political accountability. War is easier when rulers can hide its costs, borrow without scrutiny, censor opposition and treat soldiers as instruments of state ambition. Representative institutions change that calculation. Citizens who pay taxes, lose relatives, face conscription and bear economic disruption have reasons to demand justification. In that setting, public consent changes the route to war by making leaders expose objectives, costs and risks before violence becomes policy.

Commerce supplies another route, because it changes what rulers and social groups can gain from conquest. Conquest looks more attractive when territory gives rulers exclusive access to economic life. Open commerce can reduce that incentive because wealth becomes tied to exchange rather than direct control. If a country can trade and invest under general rules, seizing territory may destroy the very networks that make prosperity possible.

Law contributes by making expectations and violations more public. That premise runs into an immediate difficulty: international law cannot work like domestic criminal law because there is no global police force with monopoly authority. Even so, law can clarify obligations and violations. It can also help governments coordinate protest, retaliation and justification. The effect is practical: a treaty can define a breach, a court can turn complaints into public claims, and diplomatic rules can coordinate protest or compliance.

Institutions extend that logic through regular practice. Because states return to the same forums, work through known procedures and leave records of their promises, they reduce the need to invent a new diplomatic machinery for every dispute. Institutions can also keep communication open during crises, when misperception can turn fear into escalation. In this sense, institutions make power more public, more predictable and more costly to abuse, which is why they matter even when they cannot command states like a government.

Main Authors and Their Perspectives

Immanuel Kant gave liberal IR its most influential peace mechanism. In Perpetual Peace, he argued that peace had to be established through political and legal reform. For Kant, a republican constitution restrains rulers because citizens who finance and suffer war cannot be excluded from the decision to authorize it. A federation of free states, in his sense, lets states bind themselves to rules against war without turning them into one empire. Kant also used the term cosmopolitan right for a limited right of hospitality: foreigners should not be treated as enemies simply because they arrive on another state’s territory. Kant’s peace is built step by step: rulers become answerable to citizens, states gain a legal alternative to empire, and foreigners receive minimal protection when they meet another state’s authority.

Richard Cobden and the Manchester School developed the free-trade version of liberal peace. Cobden treated protectionism, empire and militarism as connected problems. Tariffs favored organized producers at the expense of consumers. Colonies and protected markets encouraged naval spending, strategic rivalry and political privilege. Free trade, by contrast, weakened the claim that prosperity required territorial control. In his version, commerce becomes an anti-imperial mechanism: open exchange lowers the political value of conquest because access no longer depends on possession or protected markets.

Norman Angell sharpened the economic argument before World War I in The Great Illusion. He is often misread as claiming that interdependence had made war impossible because governments would rationally avoid the enormous economic costs of war and conquest. Angell’s argument was narrower and more useful for classical liberalism: modern conquest could become economically futile even when a victorious army controlled territory.

The reason was that modern wealth was not just land, buildings or raw materials waiting to be seized. A large part of it depended on confidence that debts would be paid, contracts would be honored, factories would receive inputs, workers would keep producing and banks would keep credit flowing. An invading army could occupy a city, but occupation could frighten lenders, interrupt payment systems, close markets and disrupt the cooperation that made the economy valuable. In that sense, the conqueror could destroy wealth more easily than it could possess it. World War I exposed the limit of this reasoning. A government can accept economic damage when leaders believe national survival is at stake. Nationalist mobilization can make compromise look dishonorable, while alliance obligations and military timetables can force decisions before commercial interests organize restraint. Even so, Angell clarified a lasting liberal mechanism: as economies become harder to appropriate by force, conquest can lose some of its economic reward even when it remains politically possible.

Woodrow Wilson turned liberal principles into a postwar diplomatic program. The Fourteen Points became a way to translate liberal ideas into diplomatic practice. Open diplomacy was meant to reduce secret bargaining that could commit societies to war without public knowledge. Self-determination challenged the idea that peoples could be transferred among empires as diplomatic property, although Wilson applied it unevenly. Collective security gave the program its institutional ambition: aggression was supposed to become a common concern for members of an organized peace, not only a problem for the direct victim. The League of Nations was created to make that promise permanent. Its weakness became visible because the United States never joined, member states controlled the military force and economic sanctions the League needed, and aggressors in the 1930s learned that condemnation did not always lead to effective action. For liberal IR, the failure mattered because it showed that collective security needs legal rules plus states willing and able to enforce them.

Michael Doyle, John Oneal and Bruce Russett brought Kantian themes into modern democratic peace research. Doyle’s contribution was to turn Kant’s republican mechanism into the modern democratic peace claim: liberal states may form a “separate peace” among themselves because they recognize one another as lawful and accountable, even though they have often fought non-liberal states. Oneal and Russett then converted that older logic into empirical research. They asked whether democracies, economically connected states, and states tied through international organizations were less likely to enter militarized disputes. Their contribution was methodological as well as theoretical: liberal claims about restraint became propositions that could be tested against realist explanations based on power and anarchy.

Andrew Moravcsik later reformulated liberal theory around state preferences. In "Taking Preferences Seriously", he argues that liberal IR theory begins with state-society relations: domestic and transnational social actors shape the purposes governments pursue. This formulation keeps liberalism from being reduced to optimism about peace. In practical terms, Moravcsik’s version explains both cooperation and conflict by asking whose preferences the state represents and how those preferences enter foreign policy.

Classical Liberalism vs Realism

The clearest difference between classical liberalism and classical realism is the starting point of explanation. Realists usually begin with anarchy, survival and power. They also emphasize the security dilemma: one state may arm itself for defense, but other states can read that preparation as a threat and respond with their own arms or alliances. Classical liberals ask a prior question: what do states want, and how did those wants become policy? The two approaches can describe the same crisis, but they look for causation in different places.

For realists, the distribution of power usually carries more explanatory weight than domestic politics. A state surrounded by threats must respond to danger regardless of its regime type. For classical liberals, regime type and domestic representation affect how danger is interpreted and who benefits from a chosen response. In this respect, realism explains why insecurity pushes states toward self-help. Classical liberalism explains why some states turn insecurity into militarization, while others try to reduce risk by making commitments public, tying domestic groups to continued exchange or bargaining through institutions before fear escalates.

The two theories also disagree over institutions. Realists tend to see institutions as reflections of state power and interest. Institutions survive when powerful states support them and fail when those states defect or when the balance of power changes. Classical liberals accept that institutions depend on state support, but they give institutions additional causal weight. For them, rules turn some private defections into public violations, raising costs in domestic and diplomatic arenas. A government that violates a public agreement may still get away with it, yet the violation creates diplomatic and domestic consequences that would not exist in a purely private bargain.

Finally, the theories differ over gains from cooperation. Realists worry that a partner’s larger gain can later become a security threat. Classical liberals give more room to absolute gains, especially outside immediate survival questions. If a commercial agreement makes both sides wealthier, or if an institution reduces a shared vulnerability, the bargain can be rational even when benefits are uneven. The liberal answer is strongest when the issue creates repeated interaction and domestic groups value the benefits enough to defend cooperation across political cycles.

Modern Developments

Modern liberal IR theory expanded the classical tradition in several directions. Democratic peace theory turned Kant’s republican idea into an empirical question: are liberal democracies especially unlikely to fight one another? The most careful versions treat elections as only one part of a wider mechanism. They ask whether constitutional checks slow presidents, prime ministers and cabinets, whether civil liberties let opposition criticize war and whether liberal governments expect one another to settle disputes lawfully.

Commercial liberalism also changed. Older writers focused on free trade as a restraint on conquest and empire. Later work examined how trade creates domestic groups with a stake in openness and how dependence on foreign markets, energy or finance can become a source of leverage. This development makes the theory more useful, but it also exposes a vulnerability. In practice, interdependence can restrain conflict when actors value continued exchange. It can intensify conflict when states turn economic access into pressure and coercive leverage.

Neoliberal institutionalism developed the institutional side of liberal thought after realism became dominant in the discipline. Robert Keohane and Joseph Nye’s account of complex interdependence showed how societies interact through many channels beyond foreign ministries. In that setting, firms shape investment, regulators negotiate standards, courts interpret obligations and international organizations organize information. For issues such as trade rules, environmental policy or technical standards, military force often does not solve the problem at stake. What becomes more useful is the ability to observe whether states comply, share information about violations and keep bargaining after one agreement creates new disputes.

Liberal internationalism grows from the same family but is broader than classical liberalism. It often treats democracy, rights, open markets and collective security as parts of a larger international order. Classical liberalism shares many of those commitments, yet it remains more suspicious of coercive transformation and centralized authority. From a classical liberal perspective, an international order should be judged by whether it limits arbitrary power. If it gives powerful states and officials new authority to rule in the name of liberal goals, it recreates the problem it claims to solve.

Criticism and Limits

The strongest criticism of classical liberalism comes from realism. From a realist perspective, anarchy can make even peaceful intentions look dangerous because no state can be certain how another will use future gains. That suspicion appears inside cooperation itself: a state may prefer trade or legal rules, but it still has to ask what happens if the other side uses the agreement to gain military advantage. The same logic limits liberal claims about institutions: they may reduce uncertainty in ordinary disputes, yet they cannot enforce commitments when major powers decide that vital interests are at stake. Accordingly, the realist critique narrows the conditions under which liberal mechanisms can operate without denying that those mechanisms sometimes work.

The commercial peace argument also faces a visible historical problem. The world before 1914 had extensive trade, finance and communication, and it still entered a catastrophic war. For critics, that experience shows the limit of economic restraint: states may accept enormous commercial losses when leaders and publics believe that security, status or ideological commitments are at stake.

Classical liberalism also faces a problem of inequality. Formal freedom of exchange can hide unequal bargaining power among states, firms and social groups. A formally neutral rule can favor a firm or state that already has capital to invest, lawyers able to use the rule and market access where the gains can be captured. If the gains from openness are concentrated while losses are imposed on vulnerable groups, a liberal order can lose the domestic consent on which liberal restraint depends, and protectionism or nationalist politics can grow from that loss.

A separate limit appears when liberal language is used to justify empire or intervention. Liberal arguments have often opposed imperial rule, but powerful states have also claimed to spread rights or democracy while imposing domination on weaker societies. The 2003 Iraq War became a major warning for this reason: democracy promotion by force can destroy the legitimacy that liberal institutions are supposed to require. Consequently, liberal peace depends on domestic consent and legal restraint rather than liberal vocabulary alone, especially when powerful states claim to act for liberal ends.

There is also a sovereignty tension. Liberalism cares about individuals inside states, rather than governments alone. That concern supports human rights claims and, in some cases, arguments for humanitarian protection or democracy promotion. However, intervention can violate self-determination and create new forms of dependency. Classical liberalism is especially alert to this danger because it distrusts power that claims moral exemption from ordinary limits.

Conclusion

In International Relations, classical liberalism explains how the conditions of war and cooperation can be altered. It accepts that states live without a world sovereign, but it does not treat anarchy as the only cause of foreign policy. It traces the path from domestic society to state preferences. It also explains why commerce can lower the reward of conquest, why public opinion can restrain rulers, and why law and institutions can make peaceful bargaining more credible.

The strongest lesson is conditional. Market exchange, democratic accountability and international organization restrain violence only when they change incentives and make coercion visible. Classical liberalism teaches that peace requires mechanisms that force rulers to justify costs, make exchange more valuable than conquest, and turn some disputes into public legal or institutional procedures. Those mechanisms can fail when nationalist politics makes compromise dishonorable, when leaders fear strategic loss, when inequality undermines consent, when empire hides behind liberal language, or when great-power rivalry overwhelms legal restraint. Even when they fail, they retain analytical force because they show that international politics is more than a struggle over power. It is also a struggle over the rules and domestic conditions that decide how power may be used.