But the effort required had been too great to cease when its purely defensive purpose had been achieved by the defeat of Napoleon. Now, a hundred years later, they are still engaged in the same movement, which has become one of aggression and conquest. Whether we are now seeing the end of the movement it is not yet possible to guess. If men had any strong sense of a community of nations, nationalism would serve to define the boundaries of the various nations. But because men only feel community within their own nation, nothing but force is able to make them respect the rights of other nations, even when they are asserting exactly similar rights on their own behalf. Analogous development is to be expected, with the course of time, in the conflict between capital and labor which has existed since the growth of the industrial system, and in the conflict between men and women, which is still in its infancy. What is wanted, in these various conflicts, is some principle, genuinely believed, which will have justice for its outcome. The tug of war of mutual self-assertion can only result in justice through an accidental equality of force. It is no use to attempt any bolstering up of institutions based on authority, since all such institutions involve injustice, and injustice once realized cannot be perpetuated without fundamental damage both to those who uphold it and to those who resist it. The damage consists in the hardening of the walls of the Ego, making them a prison instead of a window. Unimpeded growth in the individual depends upon many contacts with other people, which must be of the nature of free coöperation, not of enforced service. While the belief in authority was alive, free coöperation was compatible with inequality and subjection, but now equality and mutual freedom are necessary. All institutions, if they are not to hamper individual growth, must be based as far as possible upon voluntary combination, rather than the force of the law or the traditional authority of the holders of power. None of our institutions can survive the application of this principle without great and fundamental changes; but these changes are imperatively necessary if the world is to be withheld from dissolving into hard separate units each at war with all the others. The two chief sources of good relations between individuals are instinctive liking and a common purpose. Of these two, a common purpose might seem more important politically, but, in fact, it is often the outcome, not the cause, of instinctive liking, or of a common instinctive aversion. Biological groups, from the family to the nation, are constituted by a greater or less degree of instinctive liking, and build their common purposes on this foundation.