A neutral state may at any time lay aside its neutrality and engage in war. This is recognized, though with a somewhat mediaeval flavor, by Macchiavelli in his counsel to the ideal prince, where he advises the latter never to remain neutral in a war between his neighbors, but to join with one side or the other, since by his aid that side would gain the victory and he could share in the spoil.

However unlikely it may be that such motives would bear weight to-day, it is nevertheless true that the right to make war at will exists in every sovereign state unless, by reason of international agreement, it is placed altogether outside of the realm of war and devoted to perpetual peace. The duties of simple, or self-imposed neutrality are now clearly recognized and quite generally observed. The neutral state must maintain exclusive jurisdiction and sovereignty over its land and territorial waters, and is bound as well to prevent within its borders all acts inconsistent with complete impartiality toward belligerents. It must, moreover, regulate the use of its harbors and coaling stations according to the recognized provisions of international law; it is bound to prevent the enlistment within its borders of troops destined for foreign service, and, finally, it is compelled to acquiesce in the penalties incurred by its subjects when engaged in the carriage of contraband goods, breach of blockade, or resistance to the belligerent rights of stoppage, visit and search.