The Re-Emergence of Conquest: International Law and the Legitimate Use of Force


The re-emergence of the issue of conquest of territory is one of the most contentious debates surrounding contemporary international law. This article investigates certain developments in respect territorial conquests and the reaction of the international community to such acts. There is analysis of the key relationship between conquest and empire and speculates on the possibility that the re-emergence of conquest is further evidence that international society is reverting to a previous incarnation whereby Great Power politics is assuming its former pre-eminence, at the expense of the rules-based system which emerged after the Second World War. The article places conquest within the wider context of international law whilst discussing historical occurrences and contemporary instances.

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  1. 1.

    Conquest has, in effect, two components. The first is the annexation of territory followed by the subjugation of its inhabitants. With that, the territory comes under the sovereignty of the conqueror. This in contrast to mere occupation of territory were sovereignty is not transferred to the invader. As Thomas Lawrence noted ‘Annexation alone is incapable of giving good title’ (Lawrence, 1929).

  2. 2.

    In the contemporary cases of Daesh, and the so-called Occupied Territories of former Palestine, what is unusual is that in the first instance ISIS is a non-state actor attempting to acquire territory through conquest and in the second the Palestinian Authority, which is not a universally recognised state, is having its territory annexed by Israel.

  3. 3.

    ‘In traditional legal terms, conquest was measured by the principle of debellatio, the complete subjugation of a belligerent nation or people, resulting in an irreparable loss of sovereignty and forfeiture of freedom’ (Sen, 2013).

  4. 4.

    See generally UN Charter, Arts. 2(4) and 51; Declaration on Principles of International Law Concerning Friendly Relations and Co-operation among States in accordance with the Charter of the United Nations, GA Res. 2625, Annex, 25 UN GAOR, Supp. (No. 28), UN Doc. A/5217 (1970) at 121.

  5. 5.

    Thomas Baty doubted the commonly formulated proposition that seventeenth and eighteenth century international law permitted an invader to assume sovereign rights over territory upon achieving effective control (Baty, 1927).

  6. 6.

    As Jo-Ann Pemberton observed, ‘Although Grotius listed wars of imperial expansion as among the unjust causes of war and Vattel condemned conquest on moral grounds, they also understood that as long as conquest was an accepted feature of state practice there was a need to legally institutionalise it’ (Pemberton, 2009).

  7. 7.

    As Hersch Lauterpact observed ‘A number of writers, e.g., Oppenheim, hold that, in a strict sense, not conquest, but subjugation, confers the valid title, but for the purposes of this paper the distinction is unimportant. As Oppenheim says: "But the validity of the title of the subjugating state does not depend upon recognition on the part of other Powers”’(Lauterpact, 1937).

  8. 8.

    The law of Belligerent occupation is governed by the Hague Regulations of 1907, as well as by the Fourth Geneva Convention of 1949, and the customary laws of belligerent occupation.

  9. 9.

    Nehal Bhuta noted that ‘Hersch Lauterpacht dates the first usage of ‘belligerent occupation’ to 1844, in the writings of the German publicist Hefter. 22 Occupatio bellica develops as a legal status defined in contraposition to debellatio. The former is quintessentially a temporary state of facts arising when an invader achieves military control of a territory and administers it on a provisional basis, but has no legal entitlement to exercise the rights of the absent sovereign. The latter is a legal category describing a condition of ‘ subjugation’ in which the original sovereign is not merely temporarily incapacitated from exercising his powers due to the presence of the occupying military forces, but is completely defeated: his institutions of state destroyed, his international legal personality dissolved, with no allies continuing to fight on his behalf’(Bhuta, 2005).

  10. 10.

    An example of cession would be therefore the transfer by peace treaty of Alasce-Lorraine to Germany by France at the end of the Franco -Prussian war in 1871.

  11. 11.

    Declaration of Principles of International Law Concerning Friendly Relations and Co-operation Among States in Accordance With the Charter of the United Nations, G.A. Res. 2625 (1970) (‘No territorial acquisition resulting from the threat or use of force shall be recognized as legal.”); Third Report on State Responsibility: Report by Special Rapporteur James Crawford, at 23, para. 410 (2000) (‘States may not recognize as lawful, for example, a unilateral acquisition of territory procured by the use of force, even if the use of force was arguably lawful’.).

  12. 12.

    This is, as discussed later in the article, arguably the stance that Israel has taken towards the so-called occupied territories.

  13. 13.

    As Pagden notes: ‘Conquest, even when it was practiced by many states, still carried the burden of illegitimacy. Even the Spanish, whose American empire was so obviously based on conquest, and who boasted a rich imaginative literature to prove it, banned all official use of the word in 1680′. The word conquest was thus absent from ‘Nueva Recopilación de leyes de los reinos de las Indias’, Bk. 4 Tit. I Ley 6, in S. Lyman Tyler, Spanish Laws concerning Discoveries, Pacifications, and Settlements among the Indians: With an Introduction and the First English Translation of the New Ordinances of Philip II, July 1573, and of Book IV from the Recopilación de leyes de los reinos de las Indias relating to these subjects (Salt Lake City, Utah: American West Center, University of Utah, 1980) cited in Pagden (2005).

  14. 14.

    As Gilmartin notes, ‘…central to this story of the fact that the idea of Law as an alternative foundation for sovereignty came most powerfully from the other side of the Eurasian ecumene, that is, from the British themselves. Though the British initially engaged with old forms of Mughal sovereignty in order to legitimise their own regime (and even gave them a legal gloss through a recognition of what some called an ‘ancient Mughal constitution), they had already begun by the late eighteenth century to move, amid much contestation, to a rhetoric of sovereign legitimation associated with what had increasingly come to be called the ‘rule of law’ (Gilmartin, 2017).

  15. 15.

    However, as Jo - Anne Pemberton has remarked: ‘In theory, the principle of cession is compatible with an anti-imperial reading of sovereignty because it involves the voluntary surrender of territory to another party rather than its forced occupation, although we know in practice the distinction between the former and the latter was extremely slippery’ (Pemberton, 2009).

  16. 16.

    There was a considerable amount of work written in support of Britain’s imperial expansion in India based on realpolitik. See, for example the justification provided by Robert Orme for Robert Clive’s conquest of Bengal in 1764 (Orme, 1778).

  17. 17.

    C. 9054 (1898) 5 quoted by Michael Lindley (Lindley,1926).

  18. 18.

    Milner et al.(eds) History of the American West (Oxford University Press, 1994) p.161.

  19. 19.

    Johnson & Graham’s Lessee v McIntosh (21 U.S. (8 Wheat.) 543 (1823).

  20. 20.

    American Insurance v Canter (1828) 1 Peters 511.

  21. 21.

    Ibid. Treaty making and transfer of territory was not limited to Native tribes. Having defeated Mexico, the United States received California and New Mexico through cession by virtue of the Treaty of Guadalupe Hidalgo signed on 2 February 1848.

  22. 22.

    The Monroe Doctrine, announced by President James Monroe on 2 December 1823, ostensibly made the United States guardian of its neighbours against imperial encroachment from the European Powers. Latterly, it was interpreted by the US as a right to intervene in Latin American affairs if its, largely economic, interests were threatened.

  23. 23.

    Article X Covenant of the League of Nations 1919.

  24. 24.

    Treaty between the United States and other Powers providing for the renunciation of war as an instrument of national policy. Signed at Paris, August 27, 1928; ratification advised by the Senate, January 16, 1929; ratified by the President, January 17, 1929; instruments of ratification deposited at Washington by the United States of America, Australia, Dominion of Canada, Czechoslovkia, Germany, Great Britain, India, Irish Free State, Italy, New Zealand, and Union of South Africa, March 2, 1929: By Poland, March 26, 1929; by Belgium, March 27 1929; by France, April 22, 1929; by Japan, July 24, 1929; proclaimed, July 24, 1929.

  25. 25.

    Referring to the military operations between China and Japan in South Manchuria, Mr. Stimson notified those countries on January 7, 1932, that the United States: "cannot admit the legality of any situation de facto nor does it intend to recognize any treaty or agreement entered into between those Governments, or agents thereof, which may impair the treaty rights of the United States or its citizens in China, including those which relate to the sovereignty, the independence, or the territorial and administrative integrity of the Republic of China, or to the international policy relative to China, commonly known as the open-door policy; and that it does not intend to recognize any situation, treaty, or agreement which may be brought about by means contrary to the covenants and obligations of the Pact of Paris of August 27,1928, to which treaty both China and Japan, as well as the United States are parties." Department of State Press Releases, No. 119 (Jan. 9, 1932), pp. 41–42.

  26. 26.

    It was widely accepted that there was an obligation to recognise a new state if it had been legally constituted by cession or other means (Orakhelashivili, 2019). However, states that emerged through illegal acts were also recognised at times.

  27. 27.

    Department of State Press Releases, No. 136 (May 7, 1932), p. 41.

  28. 28.

    Ibid. The dictum was confirmed in Article 11 of the Convention on Rights and Duties of States, signed at the Seventh Pan American Conference in Montevideo on 26 December, 1933: ‘The contracting States definitely establish as the rule of their conduct the precise obligation not to recognize territorial acquisitions or special advantages which have been obtained by force whether this consists in the employment of arms, in threatening diplomatic representations, or in any other effective coercive measure. The territory of a State is in violable and may not be the object of military occupation nor of other measures of force imposed by another State directly or indirectly or for any motive whatever even temporarily’.

  29. 29.

    The Italian aim, as with France’s invasion of Algeria in 1830, was to a large extent based on national aggrandisement.

  30. 30.

    Further opprobrium was placed on those actors who had attempted to instigate conquest through the development of the prohibition on waging a war of aggression. Perpetrators of this act were tried at the International Military Tribunal at Nuremberg in the aftermath of the Second World War. Discomfort for the allied prosecutors did occur when one of the senior Nazi leaders on trial, Hermann Goering, compared Germany’s acts to those of the imperial powers Britain and France. More recently, waging a war of aggression has, since 2010, been included as one of the acts that come under the jurisdiction of Article 8 bis of the Rome Statute of the International Criminal Court.

  31. 31.

    Georg Schwarzenberger has observed that ‘Under the consensual quasi-orders of the United Nations and the Kellogg Pact, the moral distinction between just and unjust wars, evolved by canonical and naturalist jurists, has been transferred into one between legal and illegal war’. (Schwartzenberger 1960).

  32. 32.

    Hazel Fox provides a concise definition of a peremptory norm: ‘Some laws are given superior rank, are described as peremptory permitting no derogation: based on jus cogens, they are considered as universally obligatory without express consent’ (Fox 2007).

  33. 33.

    As Peter Sluglett noted ‘Iraq's claim to Kuwait rests largely on the fact that, at various times in the nineteenth century, Kuwait was, to a greater or lesser extent, an administrative dependency of the Ottoman Empire’s province of Basra’ (Sluglett 2002).

  34. 34.

    This was not only in the case of issues related to use of force, such as the invasion of Iraq in 2003, but more recently in relation to international trade.

  35. 35.

    In Ukraine there has allusions to so-called ‘Little Green Men’ or irregular Russian forces who do not bear official military insignia.

  36. 36.

    Although there was a treaty in place between the two states concerning access for the Russian Black Sea Fleet to Sebastapol there were allegations made by Russia, and with little justification, that Ukraine was in breach of the agreement or was intending to abrogate it. Agreement Between Ukraine and Russia on the Black Sea Fleet in Ukraine, Russia-Ukraine, 21 April 2010.

  37. 37.

    These sanctions themselves have been question and then revoked by, amongst other, US President Donald Trump as being ineffective and self-damaging.

  38. 38.

    However, as Thomas Grant notes ‘The referendum in Crimea thus differed from plebiscitary exercises elsewhere (as in former colonial setting) that were affirmed by international actors or that took place with the consent of the central authorities of the state. eg the Scotland Act 1998 (Grant, 2015).

  39. 39.

    As Grant elaborates: ‘For a territory to separate from one state and join another entails at a minimum acts in two municipal legal orders. Russia characterized the separation of Crimea from Ukraine as the result of a referendum taking place in the Crimean area of Ukraine, and its annexation as the result of a treaty between an independent Crimea and Russia’ (Grant, 2015).

  40. 40.

    Therefore, it is arguably the case that Crimea remains under the belligerent occupation of Russia and subject to the provisions of the aforementioned Hague Convention of 1907 and Fourth Geneva Convention of 1949.

  41. 41.

    Most notably Article 43 Protocol I 1977 to the Geneva Conventions.

  42. 42.

    The traditional categories of internal conflict are rebellion, insurgency and belligerency. Rebellion can be understood as use of armed force against the state authorities with insurgency being where armed groups gain control, either temporarily or permanently over part do the territory of a state. Belligerency occurs when that control is recognised either by the other party to the conflict or by external actors (Moir, 1998).

  43. 43.

    These breaches include the most extreme examples such as executing prisoners. This is in clear contradiction of the Third Geneva Convention 1949.

  44. 44.

    The objective of a Kurdistan is complicated by the fact that the Kurds are not one homogenous and division of the Kurdish people within the existing states of Iran, Iraq Turkey and Syria, but also that statehood is not an objective sought by one, united community. Rather, there is the objective for certain Kurdish groups of greater autonomy within the states in which they exist. The struggle for autonomy by the Kurds led by Abdullah Ocalan in Turkey can be characterised as an insurgency.

  45. 45.

    Golan Heights Law, 14 December 1981, Laws of the State of Israel, 36 (1982), 7.

  46. 46.

    UN Doc S/RES/476 (1980) (30 June 1980) para 3; UN Doc S/RES/478 (1980) (20 August 1980) paras 2 and 4.

  47. 47.

    Proclamation 9683 of 6 December 2017, ‘Recognizing Jerusalem as the Capital of the State of Israel Relocating the United States Embassy to Israel to Jerusalem’ Federal Register vol 82, no 236 (11 December 2017)58,331; See also, Statement by the United States before the Security Council, UN Doc S/PV.8128 (8 December 2017), 11.

  48. 48.

    Proclamation 9683 (n 2)) ibid. See also, Statement by the United States before the Security Council, UN Doc S/PV.8128 (n 2) 11 and UN Doc S/PV.8139 (18 December 2017).

  49. 49.,p.8.

  50. 50.


  51. 51.

    UNSC Resolution 2334 S/RES/2334 23 December 2016.

  52. 52.

    ‘With God’s help we will extend Jewish sovereignty to all the settlements as part of the (biblical) land of Israel as part of the State of Israel’ (Hassan, 2019).

  53. 53.,

  54. 54.

    Paradoxically, as mentioned previously there has been recent success in having the prohibition on the acts of aggression by states included in the Rome Statute of the International Court of Justice. See Article 8 bis of the Rome Statute of the International Criminal Court.

  55. 55.

    In the cases of both the Palestinian Liberation Organisation and Islamic extremists of an earlier incarnation to that of ISIS the main threat they posed was through intermittent acts of terrorism or rebellion rather than the realistic possibility of conquest.

  56. 56.

    This is also perhaps why various tribunals of international law have favoured the principle of uti posseditis in relation to Latin America and Africa and enforced the borders set by the imperial powers there in the nineteenth century and before.

  57. 57.

    Arbitrator Huber, The Island of Palmas Case (Netherlands v USA) (1928) RIAA 2 (1949), 829.

  58. 58.

    Contemporary international law is clear that use of force is only legally justified in two sets of circumstances; in self- defence and if authorised by the United Nations as contained in Articles 2(4) and 51 of the Charter of the United Nations.


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Mulligan, M. The Re-Emergence of Conquest: International Law and the Legitimate Use of Force. Liverpool Law Rev (2020).

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  • Conquest
  • Cession
  • Treaties
  • Recognition