Until the 19th century, ‘occupation’ made it possible to immediately acquire all the titles of the region by excluding the sovereignty of the territory. Until the medieval period, occupation was synonymous with ‘conquest’ or ‘exploitation’. Thus, the transfer of sovereignty through occupation included not only the territory and the public property of the country, but also all private property. However, as political and ideological changes such as the principle of balance of power, humanitarian ideology, the development of modern military organizations, and emergence of nation states, etc. appeared in the nineteenth century, the concept of traditional occupation in the same sense as conquest gradually disappeared, and the concept of occupation based on the idea of ‘​temporary control’ on the occupied territories became firmly established. Thus, ① temporality of occupation, ② the principle of the inalienability of sovereignty through sheer force, and ③ the ‘conservationist principle’ based on preservation of status quo ante in the territory were regarded as core principles of International Law of Occupation. However, the occupation of Iraq in 2003 brought a chance to trigger a debate on whether to provide adequate function as a normative framework that governs the rights and obligations of the occupant with the existing International Law of Occupation. The ‘transformative occupation' that emerged in 2003 with the occupation of Iraq is that the conservationist principle, which forms the core of the International Law of Occupation, no longer meets the demands of the times, which was linked to the argument that an alternative legal system reflecting state practice should be sought. However, the existence of the occupation is not a matter of law but merely a matter of fact. No matter how denied the status of occupying power, the effectiveness of the International Law of Occupation cannot be denied in that it is enough to establish ‘effective control’ by the occupying power. Of course, it cannot be denied that recent occupation patterns have been unusual circumstances that were not envisioned at the time of the adoption of the Hague Regulations of 1907. Nevertheless, as long as the effective control test of Article 42 of the Hague Regulations of 1907 are met, the occupying power should still be seen as being bound by the International Law of Occupation.