The international law definition of the term "occupation” refers to a "period following invasion and preceding the cessation of hostilities” that "imposes more onerous duties on an Occupying Power than on a party to an international armed conflict.”
Determining the start of an occupation is essentially a question of fact, which must be distinguished from invasion: "Invasion is the marching or riding of troops—or the flying of military aircraft—into enemy country. Occupation is invasion plus taking possession of enemy country for the purpose of holding it, at any rate temporarily. The difference between mere invasion and occupation becomes apparent from the fact that an occupant sets up some kind of administration, whereas the mere invader does not.
This distinction flows from The Hague Regulations, which has the status of customary international law, which has the status of customary international law and provides a definition of occupation upon which, on the whole, the Fourth GenevaConvention relies:
"Territory is considered occupied when it is actually placed under the authority of thehostile army. The occupation extends only to the territory where such authority has been established and can be exercised.”
The most-fundamental principles of international law and world order affirm that "It is the right and duty of all States, individually and collectively, to eliminate colonialism, apartheid, racial discrimination, neocolonialism and all forms of foreign aggression, occupation and domination, and the economic and social consequences thereof, as a prerequisite for development.”
 See Lord Arnold Duncan McNair and Sir Arthur Watts, The Legal Effects of War (Cambridge: Cambridge University Press, fourth edition, 1966), pp. 377–78; and Georg Schwarzenberger, International law as Applied by International Courts and Tribunals, Vol. II: "The Law of Armed Conflict” (London: Stevens & Sons, 1968), p. 324.
 Hersch Lauterpacht, "Disputes, war and neutrality,” in Lassa Francis Lawrence Oppenheim, International law: a treatise, Vol. II: (London: Longman, 7th edition, 1952) p. 434; see also Re Lepore, Annual Digest of Public International Law Cases, Vol. 13, p. 354 (Supreme Military Tribunal, Italy: 1946), p. 355; Disability pension case, International Law Reports, Vol. 90 (Federal Social Court, F. R. Germany: 1985), p. 403; and Gerhard von Glahn, The Occupation of Enemy Territory: A Commentary on the Law and Practice of Belligerent Occupation (Minneapolis: University of Minnesota Press, 1957), pp. 28–29.
 Article 6 of the Fourth Geneva Convention conveys a wider meaning than in Article 42 of The Hague Regulations: "So far as individuals are concerned, the application of the Fourth Geneva Convention does not depend upon the existence of a state of occupation within the meaning of Article 42 … The relations between the civilian population of a territory and troops advancing into that territory, whether fighting or not, are governed by the present Convention. There is no intermediate period between what might be termed the invasion phase and the inauguration of a stable regime of occupation. Even a patrol which penetrates into enemy territory without any intention of staying there must respect the Convention in its dealings with the civilians it meets.” Jean Pictet, ed., Commentary to Geneva Convention IV Relative to the Protection of Civilian Persons in Time of War (Geneva: ICRC, 1958), pp. 59–60. See also Guénaël Mettraux, International Crimes and the ad hoc Tribunals (Oxford: Oxford University Press, 2005), pp. 64–71; and Prosecutor v Naletilić and Martinović, supra. note1, pp. 74–75, paras. 219–21.
 See Prosecutor v. Naletilic and Martinovic (International Criminal Tribunal for the former Yugoslavia), at:
www.un.org/icty/naletilic/trialc/judgement/naltj030331-e.pdf, p. 73, para. 215. The customary nature of The Hague Regulations was declared by the International Criminal Tribunal at Nuremberg in the Trial of German Major War Criminals, Cmd. 6964 (1946) 65. Numerous other courts have affirmed the customary status of The Hague Regulations; see, for example, Krupp case (United States Military Tribunal at Nuremberg), Annual Digest of Public International Law Cases, Vol. 15, pp. 620, 622 (subsequently retitled International Law Reports, which title now applies to the entire series) R. v Finta, 1 S.C.R. 701 (Canadian High Court of Justice), International Law Reports, Vol. 82, p. 439; Affo v IDF Commander in the West Bank (Israel High Court), International Law Reports, Vol., 83, p. 163; Polyukhovich v. Commonwealth of Australia (Australian High Court), International Law Reports. Vol. 91, p. 123; Theodor Meron, Human Rights and Humanitarian Norms as Customary Law (Oxford: Clarendon Press, 1989), pp. 38–40.