A war is inevitably linked to changes in state borders, and the fighting armies were often occupying a territory of a hostile state by extending their power onto them. In the past, the areas occupied by a hostile state were often integrated to the victorious state (by the so-called deballatio) or subjected to various forms of dependence (e.g. a fief). Starting from the 19th century, a concept has been developed, according to which territorial changes between two belligerent countries are impermissible until the termination of military activities and the conclusion of a peace treaty . As a result of the Hague Conference of 1899 and 1907, an institution of an occupied territory was introduced into the language of international law, i.e. a state territory occupied by an enemy.
An annexation, being the result of war, has a different character from the institution of an occupied territory, and a military occupation has not replaced a deballatio. They both coexisted, although they stem from a similar factual situation – a state of war and a consequent intrusion of an enemy on another state's territory. They also bring a similar effect, which is to establish the political system of the occupying state in this territory. As long as war was a legal mean of settling international disputes, the resulting transfer of a territory could not be illegal. During the ‘20s and ‘30s of the 20th century, the states were applying the practice of integrating the conquered territories rather than establishing a military occupation regime, and this met with the appreciation of the then countries. However, the author of this article puts forth a thesis that at the turn of the ‘30s and ‘40s of the 20th century, there was a prohibition of deballatio effected in violation of the then international law, and therefore with the Kellogg – Briand Pact. Territorial annexations, carried out by the Third Reich and the USSR against the territory of the Republic of Poland and other European countries after 1939, were therefore illegal.
The purpose of this article is neither to comprehensively discuss the institution of military occupation, nor the prohibition of acquisition of a state territory through the use or a threat to use armed forces, or in particular – to discuss the current nature of the prohibition of deballatio. The intention of the author is to show how the prohibition of deballatio has finally emerged in the international law. When addressing this issue, it is impossible not to discuss the institution of deballatio and the international practice of the turn of the 19th and 20th centuries and the institution of military occupation, whose introduction to the international law related to the analysed issue. Only when the military occupation is presented, we will discuss the attempts aiming at prohibiting deballatio which have been made since the 19th century.
International Law and Translation in the 19th century