Is perpetual peace possible? A quick primer on Immanuel Kant and other key thinkers

Many philosophers—both historical and modern—have made significant contributions to the philosophy of peace, offering ethical, political, and metaphysical reflections on how peace can be understood, achieved, and sustained. In this short primer we focus on Kant, with more key thinkers listed below.

The main argument in Immanuel Kant’s essay Perpetual Peace: A Philosophical Sketch (1795) is that lasting global peace is possible—but only if certain rational, moral, and political conditions are met. He outlines a vision for a peaceful world order based on republican constitutions, international cooperation, and universal rights.

Core Argument

Kant argues that peace is not a natural state but something that must be actively constructed through reason and law, rather than through power or temporary treaties. He proposes a framework of “preliminary articles” (conditions to end war) and “definitive articles” (conditions to build lasting peace).

Kant’s Three Definitive Articles

1. Republican constitutions

States must be governed by republics—governments based on separation of powers and the rule of law. This ensures that citizens, who bear the costs of war, have a say in whether to go to war.

2. A federation of free states (not a global government)

Kant advocates a voluntary league or federation of independent states that commit to peaceful relations—not a world state, but a cosmopolitan legal order based on mutual respect and cooperation.

3. Universal hospitality and cosmopolitan rights

Every individual has a right to be treated without hostility when visiting a foreign country. This concept of cosmopolitan law lays the moral groundwork for global respect and peace.

Key ideas

• Peace is only just and lasting if it is built on law, freedom, and mutual respect.

• Standing armies, secret treaties, and coercive diplomacy all undermine peace.

• The potential for moral progress exists if states and individuals act according to reason and universal principles.

Kant also warns against using war as a tool of politics, anticipating many 20th-century critiques of imperialism and militarism.

Modern relevance

Kant’s Perpetual Peace influenced the development of international law, liberal democratic theory, and institutions such as the United Nations. The idea that peace requires structural reform—not just good intentions—remains deeply influential.

More thinkers to explore

Spinoza (1632–1677)

Saw peace not as the mere absence of war but as a virtue arising from strength and reason. Emphasised rational governance and freedom as conditions for social harmony.

Rousseau (1712–1778)

Although best known for The Social Contract, his critique of inequality and unjust institutions laid groundwork for later peace theories. Warned that society often corrupts natural human goodness, leading to conflict.

Tolstoy (1828–1910)

Not only a novelist but also a Christian anarchist and radical pacifist. Argued for nonviolent resistance to evil in works such as The Kingdom of God Is Within You, influencing Gandhi and Martin Luther King Jr.

Gandhi (1869–1948)

While not a philosopher in the traditional Western sense, his philosophy of nonviolent resistance (satyagraha) profoundly influenced peace theory. Merged ethical idealism with political activism.

Martin Luther King Jr. (1929–1968)

Developed a theology of nonviolence rooted in Christian ethics and Gandhian principles. Viewed peace as justice realised, not just absence of conflict.

Bertrand Russell (1872–1970)

A vocal critic of war and nuclear weapons. Argued for rationalism, internationalism, and human rights as paths to peace. Co-founded the Campaign for Nuclear Disarmament (CND).

John Rawls (1921–2002)

In The Law of Peoples (1999), extended his theory of justice to the international sphere. Proposed a framework for a realistic utopia of peaceful international cooperation, including principles for decent non-liberal societies.

Johan Galtung (1930–2024)

Sociologist and philosopher; often called the father of peace studies. Introduced concepts such as positive peace (structural justice) vs. negative peace (mere absence of violence).