§ 166. If a belligerent succeeds in occupying a part or even the whole of the enemy territory, he has realised a very important aim of warfare. He can now not only make use of the resources of the enemy country for military purposes, but can also keep it for the time being as a pledge of his military success, and thereby impress upon the enemy the necessity of submitting to terms of peace. And in regard to occupation, International Law respecting warfare has progressed more than in any other department. In former times enemy territory that was occupied by a belligerent was in every point considered his State property, with which and with the inhabitants therein he could do what he liked. He could devastate the country with fire and sword, appropriate all public and private property therein, kill the inhabitants, or take them away into captivity, or make them take an oath of allegiance. He could, even before the war was decided and his occupation was definitive, dispose of the territory by ceding it to a third State, and an instance of this happened during the Northern War (1700-1718), when in 1715 Denmark sold the occupied Swedish territories of Bremen and Verden to Hanover. That an occupant could force the inhabitants of the occupied territory to serve in his own army and to fight against their legitimate sovereign, was indubitable. Thus, during the Seven Years' War, Frederick II. of Prussia repeatedly made forcible levies of thousands of recruits in Saxony, which he had occupied. But during the second half of the eighteenth century things gradually began to undergo a change. That the distinction between mere temporary military occupation of territory, on the one hand, and, on the other, real acquisition of territory through conquest and subjugation, became more and more apparent, is shown by the fact that Vattel (III. § 197) drew attention to it. However, it was not till long after the Napoleonic wars in the nineteenth century that the consequences of this distinction were carried to their full extent by the theory and practice of International Law. So late as 1808, after the Russian troops had militarily occupied Finland, which was at that time a part of Sweden, Alexander I. of Russia made the inhabitants take an oath of allegiance,[324] although it was only by article 4 of the Peace Treaty of Frederikshamm[325] of September 17, 1809, that Sweden ceded Finland to Russia. The first writer who drew all the consequences of the distinction between mere military occupation and real acquisition of territory was Heffter in his treatise _Das Europaeische Völkerrecht der Gegenwart_ (§ 131), which made its appearance in 1844. And it is certain that it took the whole of the nineteenth century to develop such rules regarding occupation as are now universally recognised and in many respects enacted by articles 42-56 of the Hague Regulations. [Footnote 324: See Martens, _N.R._ I. p. 9.] [Footnote 325: See Martens, _N.R._ I. p. 19.]