RoT

TLDR: States have not stopped fighting wars. They have largely stopped declaring them. As aggressive war became illegal and politically toxic after 1945, governments increasingly justified military force through self-defence, collective security, parliamentary authorisation and limited “operations”. International humanitarian law wisely adapted by making armed conflict a question of fact rather than terminology. What may have been lost is something different: the formal public moment in which a government identifies an enemy, states its cause and assumes responsibility for crossing the boundary from peace to war.

This article began with a question prompted by reading Tobias Ellwood’s recent Ten Steps to Prevent World War Three, particularly Step 3, “Stop Repeating History”. [1] Korea and Vietnam both loom large in the strategic history of the United States, yet neither was accompanied by a formal declaration of war. The obvious question is when states stopped declaring wars. The more interesting one is why.

In 1907, the Hague Convention on the Opening of Hostilities required prior and explicit warning before hostilities, either through a reasoned declaration of war or an ultimatum containing a conditional declaration. [2] Declarations were never universal, and there was no golden age in which rulers politely announced every attack beforehand. What was more persistent was the expectation that war required public justification. The Yale War Manifestos Project has collected hundreds of documents issued by sovereigns between 1492 and 1945 explaining why they believed resort to war was justified. Their arguments ranged from self-defence and treaty violations to commercial interests, humanitarian claims and the balance of power. [3]

This also touches the older Just War tradition. Jus ad bellum asks whether resort to war can be justified through criteria including just cause, legitimate authority, right intention, proportionality and last resort. [4] A declaration could never make an unjust war just, but the tradition contained an important expectation: political authority had to account for its decision to use organised violence. War required not merely power, but an argument.

The twentieth century then changed the legal status of war itself. The Kellogg-Briand Pact of 1928 renounced war as an instrument of national policy, and the United Nations Charter went further after 1945. Article 2(4) prohibits the threat or use of force against another state, while Article 51 preserves individual and collective self-defence and the Security Council can authorise coercive action. [5][6] War ceased to be a normal sovereign instrument of policy, but armed force did not disappear.

This is where the disappearance of declarations becomes more than a historical curiosity. Tanisha Fazal argues that the expanding codification of the law of war created incentives for states to avoid declarations and the legal consequences associated with formally acknowledging war. [7] Katherine Irajpanah and Kenneth Schultz offer another explanation: once aggressive war became illegitimate, declaring war itself became politically counterproductive. States instead acquired a more useful vocabulary of self-defence, collective security and Security Council authorisation. [8]

The shift is dramatic. Fazal’s data suggest that declarations accompanied about 65 per cent of interstate wars in the nineteenth century but only 9 per cent after 1945. Irajpanah and Schultz apply a stricter definition and find no proper formal interstate declaration of war after 1945; they also show that 47 per cent of participants in post-1945 interstate wars instead used Security Council authorisation, an Article 51 self-defence notification, or both. [9] Governments have certainly announced that they were “at war” since then, but that is not necessarily the same legal act as issuing a declaration of war. On the stricter interpretation, 1945 marks the effective disappearance of the institution.

At almost the same moment, the Geneva Conventions made the terminology much less important for the victims of war. Common Article 2 applies not only to declared war but to any armed conflict between states, even if one party refuses to recognise a state of war. [10] This was an important humanitarian advance: a government cannot evade the law of armed conflict simply by finding another name for what its armed forces are doing.

Korea demonstrated how far the new logic could go. After North Korea crossed the 38th parallel in June 1950, President Harry Truman committed American forces under United Nations Security Council authority without seeking either a declaration of war or a prior statutory authorisation from Congress. The administration defended the intervention as an international “police action”. [11] Vietnam later proceeded under the Gulf of Tonkin Resolution rather than a declaration. Congress has issued eleven formal declarations of war in American history, all before the end of the Second World War; later major conflicts have relied on other forms of authorisation. [12][13]

The Falklands War makes the distinction unusually visible. Argentina invaded British territory in 1982, Britain sent a naval task force and the two states fought an unmistakably conventional interstate conflict. Yet Margaret Thatcher told the House of Commons on 7 April that “no formal state of war exists” between Britain and Argentina, while invoking Britain’s right of self-defence under the UN Charter. [14] By then, a state could fight something almost indistinguishable from the classical model of war without formally entering the legal condition once associated with it.

Russia did not invent this practice, although its own history shows an increasingly sophisticated use of alternative labels. During the Second Chechen War, Moscow treated a major military campaign as a “counter-terrorist operation”. The distinction made constitutional sense from the Russian perspective because Moscow regarded Chechnya as part of the Russian Federation. Yet the International Helsinki Federation for Human Rights argued in 2003 that the conflict was an armed conflict governed by international humanitarian law and criticised Russia’s consistent avoidance of that terminology, describing the counter-terrorist framework as creating an artificial legal vacuum. [15]

In Georgia in 2008, the terminology crossed into an interstate conflict. Russia described the introduction of its forces as a “peace enforcement operation”, while Georgia regarded it as aggression. [16] Six years later, Crimea added a different technique. Armed men without insignia seized strategic sites while Moscow initially denied that Russian forces were responsible. Putin subsequently acknowledged the involvement of Russian servicemen, after a referendum conducted under Russian military control had provided the political mechanism for annexation. [17] The UN General Assembly declared the referendum invalid and called on states not to recognise any alteration in Crimea’s status. [18] In the Donbas, Russia continued to obscure the extent of its direct military role while supporting separatist forces.

The “special military operation” announced on 24 February 2022 therefore had precedents in Russian practice. Putin did not simply avoid the word war; he explicitly invoked Article 51 of the UN Charter and presented Russia’s actions as collective self-defence. [19] The legal argument was overwhelmingly rejected, with 141 members of the UN General Assembly voting to deplore Russia’s aggression against Ukraine and demand the withdrawal of Russian forces. [20]

This is where comparison with Western practice requires precision. Russia’s insistence that its invasion was merely a “special military operation” was rightly ridiculed, particularly as Moscow also sought to suppress domestic descriptions of the invasion as a war. Yet the underlying reluctance to formally declare war is hardly uniquely Russian. Korea was defended as a police action, American conflicts have routinely proceeded under statutory authorisations, and Britain fought Argentina while explicitly denying the existence of a formal state of war. The comparison concerns political language and institutional form, not the legality of the respective conflicts. Britain was responding to an Argentine invasion, Korea operated under Security Council authority, while Russia’s Article 51 justification for invading Ukraine was overwhelmingly rejected.

The more interesting question is therefore what disappeared with the declaration itself. International humanitarian law gained much by becoming independent of terminology. The possible loss lies instead in political accountability. A declaration once concentrated several uncomfortable questions into a public act: who is the enemy, what has that enemy done, who has the authority to use force, why are non-military alternatives insufficient, and what political outcome is the war meant to achieve? These questions closely resemble the concerns of jus ad bellum. Historical declarations and war manifestos were often selective or dishonest, but even propaganda acknowledges the principle that an explanation is owed.

Modern governments still provide explanations through parliamentary debates, Article 51 notifications, Security Council resolutions, presidential addresses and statutory authorisations. What has largely disappeared is the single political moment at which a state acknowledges that it has crossed from peace into war. This may matter especially in democracies, where military commitments can grow incrementally: advisers become participants, defensive missions expand and temporary deployments become enduring commitments. The absence of a declaration does not abolish democratic oversight, but it can make the threshold harder to recognise.

There is a striking parallel at the other end of conflict. Fazal found that more than 70 per cent of interstate wars ending before 1950 were accompanied by peace treaties, compared with roughly 15 per cent after 1950. [21] The two trends need not have the same cause, but together they illustrate how far the traditional binary between peace and war has weakened. Korea remains an obvious example: the fighting stopped with an armistice in 1953, yet no peace treaty followed.

The old model imagined a recognisable transition from peace into war and eventually back into peace. Contemporary conflicts are more likely to pass through crises, operations, armed conflicts, ceasefires and unresolved confrontations. This helps explain why contemporary Just War Theory increasingly considers not only jus ad bellum and jus in bello, but also questions of how wars should end and what justice requires afterwards. [4]

The post-1945 order therefore produced both an achievement and an ambiguity. It delegitimised aggressive war as an ordinary instrument of state policy and ensured that humanitarian law applies regardless of what belligerents choose to call their violence. At the same time, the political boundary between war and peace became less explicit. This is not an argument for mechanically resurrecting declarations of war, which would make military action neither wiser nor more lawful. It is an argument for preserving the principle behind them: a government that resorts to organised violence should have to explain whom it is fighting, why force is necessary, under whose authority it acts and what political end it seeks.

A world in which governments no longer consider war a normal sovereign right is preferable to one in which declarations of war were routine instruments of statecraft. But the disappearance of the declaration should not be mistaken for the disappearance of war.

Sources

[1] Ellwood, Tobias. Ten Steps to Prevent World War Three. Blink Publishing, 2026.
https://www.bonnierbooks.co.uk/books/blink-publishing/ten-steps-to-prevent-world-war-three/

[2] Convention (III) Relative to the Opening of Hostilities. The Hague, 18 October 1907, Article 1. International Committee of the Red Cross, IHL Databases.
https://ihl-databases.icrc.org/en/ihl-treaties/hague-conv-iii-1907/article-1

[3] Hathaway, Oona A., William Holste, Scott J. Shapiro, Jacqueline Van De Velde, and Lisa Wang. War Manifestos Database. Yale Law School, 2017.
https://documents.law.yale.edu/manifestos

[4] Lazar, Seth. “War.” Stanford Encyclopedia of Philosophy.
https://plato.stanford.edu/entries/war/

[5] General Treaty for Renunciation of War as an Instrument of National Policy (Kellogg–Briand Pact), Paris, 27 August 1928. U.S. Department of State, Office of the Historian.
https://history.state.gov/historicaldocuments/frus1928v01/d133

[6] United Nations. Charter of the United Nations, 1945, Articles 2 and 51.
https://www.un.org/en/node/125814

[7] Fazal, Tanisha M. “Why States No Longer Declare War.” Security Studies 21, no. 4 (2012): 557–593.
https://doi.org/10.1080/09636412.2012.734227

[8] Irajpanah, Katherine, and Kenneth A. Schultz. “Off the Menu: Post-1945 Norms and the End of War Declarations.” Security Studies 30, no. 4 (2021): 485–516.
https://doi.org/10.1080/09636412.2021.1979842

[9] O’Mahoney, Joseph. “The Ripple Effects of the Illegitimacy of War.” International Studies Quarterly 68, no. 3 (2024): sqae082.
https://doi.org/10.1093/isq/sqae082

[10] Convention (I) for the Amelioration of the Condition of the Wounded and Sick in Armed Forces in the Field. Geneva, 12 August 1949, Common Article 2. International Committee of the Red Cross.
https://ihl-databases.icrc.org/en/ihl-treaties/gci-1949/article-2

[11] Library of Congress. “International Police Action and the Korean War.” Constitution Annotated.
https://constitution.congress.gov/browse/essay/ArtI_S8_C11_2_5_9/ALDE_00013924/

[12] Library of Congress. “Presidential and Congressional Power in the Vietnam War.” Constitution Annotated.
https://constitution.congress.gov/browse/essay/artI-S8-C11-2-5-10/ALDE_00013925/

[13] United States Senate Historical Office. “About Declarations of War by Congress.” United States Senate.
https://www.senate.gov/about/powers-procedures/declarations-of-war.htm

[14] Thatcher, Margaret. Statement on the Falkland Islands, House of Commons, 7 April 1982. Hansard.
https://api.parliament.uk/historic-hansard/commons/1982/apr/07/falkland-islands

[15] International Helsinki Federation for Human Rights. “IHF Intervention to the 2003 OSCE Human Dimension Implementation Meeting: Humanitarian Issues and Other Commitments: International Humanitarian Law.” 10 October 2003.
https://cdn.osce.org/sites/default/files/f/documents/f/2/42587.pdf

[16] United Nations Secretary-General. Report of the Secretary-General on the Situation in Abkhazia, Georgia. S/2008/631, 3 October 2008.
https://digitallibrary.un.org/record/638394?ln=en

[17] European Court of Human Rights. Ukraine v. Russia (re Crimea), Applications nos. 20958/14 and 38334/18, Grand Chamber Judgment, 25 June 2024.
https://hudoc.echr.coe.int/?i=001-235139

[18] United Nations General Assembly. “Territorial Integrity of Ukraine.” Resolution A/RES/68/262, 27 March 2014.
https://digitallibrary.un.org/record/767883?ln=en

[19] Russian Federation. Letter dated 24 February 2022 from the Permanent Representative of the Russian Federation to the United Nations addressed to the Secretary-General, S/2022/154, enclosing President Vladimir Putin’s address.
https://docs.un.org/S/2022/154

[20] United Nations General Assembly. “Aggression against Ukraine.” Resolution A/RES/ES-11/1, 2 March 2022.
https://digitallibrary.un.org/record/3965290?ln=en

[21] Fazal, Tanisha M. “The Demise of Peace Treaties in Interstate War.” International Organization 67, no. 4 (2013): 695–724.
https://doi.org/10.1017/S0020818313000246

Picture credit Abbie Rowe creator QS:P170,Q17505865, Franklin Roosevelt signing declaration of war against Japan, Wikimedia Commons