matters not with what means and in what ways his authority is exercised. For instance, when in the centre of a territory a large force is established from which flying columns are constantly sent round the territory, such territory is indeed effectively occupied, provided there are no enemy forces present, and, further, provided these columns can really keep the territory concerned under control.[329] Again, when an army is marching on through enemy territory, taking possession of the lines of communication and the open towns, surrounding the fortresses with besieging forces, and disarming the inhabitants in open places of habitation, the whole territory left behind the army is effectively occupied, provided some kind of administration is established, and further provided that, as soon as it becomes necessary to assert the authority of the occupant, a sufficient force can within reasonable time be sent to the locality affected. The conditions vary with those of the country concerned. When a vast country is thinly populated, a smaller force is necessary to occupy it, and a smaller number of centres need be garrisoned than in the case of a thickly populated country. Thus, the occupation of the former Orange Free State and the former South African Republic became effective in 1901 some time after their annexation by Great Britain and the degeneration of ordinary war into guerilla war, although only about 250,000 British soldiers had to keep up the occupation of a territory of about 500,000 square miles. The fact that all the towns and all the lines of communication were in the hands and under the administration of the British army, that the inhabitants of smaller places were taken away into concentration camps, that the enemy forces were either in captivity or dispersed into comparatively small guerilla bands, and finally, that wherever such bands tried to make an attack, a sufficient British force could within reasonable time make its appearance, was quite sufficient to assert British authority[330] over that vast territory, although it was more than a year before peace was finally established. [Footnote 328: See, for instance, Hall, § 161. This was also the standpoint of the delegates of the smaller States at the Brussels Conference of 1874 when the Declaration of Brussels was drafted.] [Footnote 329: This is not identical with so-called _constructive_ occupation, but is really _effective_ occupation. An occupation is constructive only if an invader declares districts as occupied over which he actually does not exercise control--for instance, when he actually occupies only the capital of a large province, and proclaims that he has thereby occupied the whole of the province, although he does not take any steps to exercise control over it.]