In order to prevent war and at the same time preserve liberty it is necessary that there should be only one military State in the world, and that when disputes between different countries arise, it should act according to the decision of a central authority. This is what would naturally result from a federation of the world, if such a thing ever came about. But the prospect is remote, and it is worth while to consider why it is so remote. The unity of a nation is produced by similar habits, instinctive liking, a common history, and a common pride. The unity of a nation is partly due to intrinsic affinities between its citizens, but partly also to the pressure and contrast of the outside world: if a nation were isolated, it would not have the same cohesion or the same fervor of patriotism. When we come to alliances of nations, it is seldom anything except outside pressure that produces solidarity. England and America, to some extent, are drawn together by the same causes which often make national unity: a (more or less) common language, similar political institutions, similar aims in international politics. But England, France, and Russia were drawn together solely by fear of Germany; if Germany had been annihilated by a natural cataclysm, they would at once have begun to hate one another, as they did before Germany was strong. For this reason, the possibility of coöperation in the present alliance against Germany affords no ground whatever for hoping that all the nations of the world might coöperate permanently in a peaceful alliance. The present motive for cohesion, namely a common fear, would be gone, and could not be replaced by any other motive unless men’s thoughts and purposes were very different from what they are now. The ultimate fact from which war results is not economic or political, and does not rest upon any mechanical difficulty of inventing means for the peaceful settlement of international disputes. The ultimate fact from which war results is the fact that a large proportion of mankind have an impulse to conflict rather than harmony, and can only be brought to coöperate with others in resisting or attacking a common enemy. This is the case in private life as well as in the relations of States. Most men, when they feel themselves sufficiently strong, set to work to make themselves feared rather than loved; the wish to gain the good opinion of others is confined, as a rule, to those who have not acquired secure power. The impulse to quarreling and self-assertion, the pleasure of getting one’s own way in spite of opposition, is native to most men. It is this impulse, rather than any motive of calculated self-interest, which produces war, and causes the difficulty of bringing about a World-State. And this impulse is not confined to one nation; it exists, in varying degrees, in all the vigorous nations of the world.