Why do states go to war, according to realists and idealists?

After the First World War, two answers to the question in the title took shape. One, later called idealist, said war came from things that could be changed, and set out to change them. The other, the realist, said it came from things that could not. Textbooks tell this as the subject's “first great debate”, though historians of the discipline have argued that no such debate took place in the form the story gives it. Each side has its founding texts. This essay quotes them where their words can be checked, and says so where they cannot.

What did the idealists propose?

A programme, and then an institution. On 8 January 1918, President Woodrow Wilson put fourteen points for the peace to the United States Congress. The first was “Open covenants of peace, openly arrived at”. The fourth asked for guarantees “that national armaments will be reduced to the lowest point consistent with domestic safety.” The last was the one that mattered most: “A general association of nations must be formed under specific covenants for the purpose of affording mutual guarantees of political independence and territorial integrity to great and small states alike.”

Read together, the points carry a diagnosis: war had come from secret bargains, from armaments, and from the lack of any body that could keep the peace. Each of those can be fixed.

The Covenant of the League of Nations was adopted on 28 April 1919, and the League began its work on 10 January 1920, when the Treaty of Versailles came into force. Under Article 10 its members “undertake to respect and preserve as against external aggression the territorial integrity and existing political independence of all Members of the League.” Article 16 gave that promise its edge: a member that went to war in disregard of its covenants “shall ipso facto be deemed to have committed an act of war against all other Members of the League.”

That is collective security: an attack on one is treated as an attack on all. The United States, whose President had proposed the league, never joined it; its Senate did not adopt the treaty.

What did Carr object to?

The idealists' central assumption. E. H. Carr's The Twenty Years' Crisis, 1919–1939 came out in September 1939, the month the Second World War began. Its fourth chapter, “The Harmony of Interests”, takes aim at the belief that the true interests of every nation agree, so that war comes only from error and can be ended by reason, law and goodwill.

Carr's reply was that no such harmony is natural. The belief in it, he argued, served the powers that gained from the existing order, by presenting their interest as everyone's. But he did not end in realism alone: the same book argues that realism without any moral aim is barren, and that sound thinking about politics needs both.

What did Morgenthau add?

A theory. Hans Morgenthau's Politics Among Nations appeared in 1948; from its second edition, in 1954, it opened with “six principles of political realism”. The first: “Political realism believes that politics, like society in general, is governed by objective laws that have their roots in human nature.” The second gives the theory its key term: “The main signpost that helps political realism to find its way through the landscape of international politics is the concept of interest defined in terms of power.”

On this reading the cause of conflict lies in human nature itself. What restrains states is not a league but the balance of power, the subject of Part Four of the book, “Limitations of National Power: The Balance of Power”.

What did Waltz change?

Where the cause is looked for. In Man, the State, and War (1959), Kenneth Waltz sorted the answers to the question in this essay's title into three “images”: the first finds the cause of war in human nature, the second in the make-up of states, the third in the system of states, which has no authority above it.

Twenty years later, in Theory of International Politics (1979), Waltz built a theory on the third image. With no government over the states, each must look after its own security, and the balance of power is what results: the subject of his chapter 6, “Anarchic Orders and Balances of Power”. This is structural realism, or neo-realism. The cause of war moves from the person to the structure.

Carr and Waltz are described here, not quoted: their books are in copyright, and their sentences could not be checked word for word against the text.

Three schools on four questions

Notice what the table shows: the idealists and Waltz both look at the system of states. They differ on whether it can be changed.

Where do India's texts stand?

They speak both languages. Article 51 of the Constitution, one of the Directive Principles, tells the State to “promote international peace and security”, to “maintain just and honourable relations between nations”, to foster respect for international law and treaty obligations, and to “encourage settlement of international disputes by arbitration”. That is the vocabulary of the Covenant.

The Arthashastra, India's classic of statecraft, states the realist logic in its Book VII: “Whoever is inferior to another shall make peace with him; whoever is superior in power shall wage war.” (Its view of power at home is set beside Machiavelli's in Is it better for a ruler to be feared than loved?)

This essay takes no side between the schools. The exam asks you to set them out from their texts and to judge; the judgement is yours.