“The principle of territorial integrity is an important part of the international legal order and is enshrined in the Charter of the United Nations, in particular in Article 2, paragraph 4” (the prohibition of the use of force), as well as in other important texts, including those on self-determination. The concept includes the inviolability of the territory of the State, including territory under the effective control and possession of a State. The International Court has held that “the scope of the principle of territorial integrity is confined to the sphere of relations between States.”  International Court of Justice, Accordance with international law of the unilateral Declaration of Independence of Kosovo, Advisory Opinion, ICJ Reports (2010), para. 80.  Ibid.
The concept of territorial integrity, if not the term, is as old as the sovereign State. It is one of the rights inherent in sovereignty and independence. Its chief importance lies in the field of the international law on the use of force (the jus ad bellum). Until the development of the general prohibition on the use of force in the first half of the Twentieth Century the territorial integrity of States was only very imperfectly protected by international law. Various ‘pacific’ uses of force were subject to limitations imposed by international law, and the Covenant of the League of Nations imposed procedural restraints. But it was only with the Kellogg-Briand Pact of 1928 that States renounced war as an instrument of national policy. In the wake of fhe Second World War, the United Nations Charter of 1945 the imposed a general prohibition on the use of force except where authorized by the Security Council, subject to the inherent right of self-defence (see Waldock).
The notion of territorial integrity is fundamental to the Westphalian State system, and underlies the contemporary rules of international law on the use of force, as embodied in the Charter of the United Nations and customary international law. Many now challenge this view of the world. The increasing importance of international human rights law, including the right of self-determination, has - it is often suggested - made this view outmoded. Yet such views are essentially of a political nature, and as a matter of law it is difficult to discern any weakening of the principle of territorial integrity. For example, it was concern for territorial integrity and the stability of borders that led the Organization of African Unity (now the African Union) to insist upon the maintenance of the colonial borders as at independence. Indeed, international law still affords a central place to territorial integrity, even in the context of self-determination. Some would even go so far as to suggest that in an age of globalization the principle of territorial integrity no longer has the importance it once has. This is a view propounded chiefly by international relations experts. Few international lawyers would agree; the International Court has recently reaffirmed that the principle is “an important part of the international legal order”. Article 2.4 of the Charter of the United Nations provides – “All Members shall refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any state, or in any other manner inconsistent with the Purposes of the United Nations.” The principle in Article 2.4, and with it the concept of territorial integrity, is repeated and elaborated on in important declarations of the UN General Assembly, including the Friendly Relations Declaration of 1970 and the Definition of Aggression of 1974. The words “against the territorial integrity and political independence of any state” were inserted into Article 2.4 of the Charter at the San Francisco Conference in 1945 in order to emphasise the importance of not infringing on territorial integrity and political independence; and they cannot be interpreted (as is occasionally suggested) as limiting the non-use of force principle embodied in the Charter. It is important to note that the concept of prohibition of the use of force, which reflects the territorial integrity principle, protects territory under a States effective control and possession, not only that over which it has de jure title. The fact that sovereignty over a piece of territory is disputed in no way entitles a State to use force to ‘recover’ territory which it claims; to do so would infringe the territorial integrity of the State in control of the disputed territory. Force may not be used “as a means of settling international disputes, including territorial disputes and problems concerning frontiers” (Friendly Relations Declaration). The territorial integrity of a State may be infringed by incursion by the armed forces of another State into its airspace and, where they exist, internal waters and (except in exercise of navigational rights) archipelagic waters and territorial sea. But it may also be infringed indirectly, such as by “organizing or encouraging the organization of irregular forces or armed bands […] for incursion into the territory of another State” (Friendly Relations Declaration), as well supporting and arming insurgents (“acts of civil strife or terrorist acts”, in the words of the Friendly Relations Declaration). Territorial integrity may also be infringed by allowing cross-border marches by organized groups of private persons. The significance of the principle of territorial integrity is underlined by the fact that, in both the UN General Assembly’s 1974 Definition of Aggression (UNGA res. 3314 (XXIX)) and the definition of “crime of aggression” adopted by the 2010 Review Conference of the Rome Statue of the International Criminal Court (Res. RC/Res.6), “aggression” or “act of aggression” means the use of armed force against inter alia the territorial integrity of another State.  International Court of Justice, Accordance with international law of the unilateral Declaration of Independence of Kosovo, Advisory Opinion, ICJ Reports (2010), para. 80.  Effective control and possession is protected through the prohibition of the use of force and not through the principle of territorial integrity (see Oscar Schachter).
One potential inroad into the notion of territorial integrity is the development of “responsibility to protect”, but this too is more a matter of policy than a legal concept. It is still too early to assess the status or impact of this notion. The UN General Assembly, in paragraph 139 of the Summit Outcome Document (resolution 60/1 of September 2005), meeting at the level of Heads of State and Government, affirmed that “we are prepared to take collective action, in a timely and decisive manner, through the Security Council, in accordance with the Charter, including Chapter VII, on a case-by-case basis and in cooperation with relevant regional organizations as appropriate, should peaceful means be inadequate and national authorities are manifestly failing to protect their populations from genocide, war crimes, ethnic cleansing and crimes against humanity.” The notion has subsequently been under continuing consideration by the UN General Assembly, and has been recalled in GA resolutions and by the Security Council. The UN Secretary General has appointed a Special Adviser, and submitted a series of reports beginning in 2009. There is a certain tension between the right of self-determination and the territorial integrity of States. In the Friendly Relations Declaration, the seventh paragraph under the heading ‘The principle of equal rights and self-determination of peoples’ (the so-called ‘safeguard clause’) provides that – “Nothing in the foregoing paragraphs shall be construed as authorizing or encouraging any action which would dismember or impair, totally or in part, the territorial integrity or political unity of sovereign and independent States conducting themselves in accordance with the principle of equal rights and self-determination of peoples as described above and thus possessed of a government representing the whole people belonging to the territory without distinction as to race, creed, or colour”. The following paragraph states categorically that “[e]very State shall refrain from any action aimed at the partial or total disruption of the national unity or territorial integrity of any other State or country[MGK/KDM2].” This tension was much discussed in the Kosovo case, but the International Court did not find it necessary to resolve the matter. A parallel principle of territorial integrity exists in the context of self-determination. In its resolution 1514 (XV), the UN General Assembly declared that “[a]ny attempt aimed at the partial or total disruption of the national unity and the territorial integrity of a country is incompatible with the Purposes and Principles of the United Nations.” And, as noted above, this is reflected in the Friendly Relations Declaration’s reference to the “territorial integrity of any State or country”.  International Court of Justice, Accordance with international law of the unilateral Declaration of Independence of Kosovo, Advisory Opinion, ICJ Reports (2010), paras. 82-83.
Declaration on the Granting of Independence to Colonial Territories and Peoples (United Nations resolution 1514 (XV) of 14 December 1960) Declaration on Principles of International Law concerning Friendly Relations and Cooperation among States in accordance with the Charter of the United Nations (United Nations General Assembly resolution 2625 (XXV) of 24 October 1970) Definition of Aggression, adopted by the United Nations General Assembly in resolution 3314 (XXIX) of 14 December 1974 H M Waldock, “The Regulation of the Use of Force by Individual States in International Law”, 81 Hague Recueil 1952, 415 Blay, “Territorial Integrity and Political Independence”, in: Max Planck Encyclopedia of Public International Law (with further references)