The simplest possible interpretation of the causes of war that might be offered is that war is a natural relation between original herds or groups of men, inspired by the predatory instinct or by some other instinct of the herd. To explain war, then, one need only refer to this instinct as final, or at most account for the origin and genesis of the instinct in question in the animal world. Some writers express this very view, calling war an expression of an instinct or of several instincts; others find different or more complex beginnings of war. Nusbaum (86) says that both offense and defense are based upon an _expansion impulse_. Nicolai (79) sees the beginning of war in individual predatory acts, involving violence and the need of defense. Again we find the migratory instinct, the instinct that has led groups of men to move and thus to interfere with one another, regarded as the cause of war, or as an important factor in the causes. Sometimes a purely physiological or growth impulse is invoked, or vaguely the inability of primitive groups to adapt themselves to conditions, or to gain access to the necessities of life. Le Bon (42) speaks of the hunger and the desire that led Germanic forces as ancient hordes to turn themselves loose upon the world. Leaving aside for the moment the question of the nature of the impulses or instincts which actuated the conduct of men originally and brought them into opposition, as groups, to one another, we do find at least some suggestion of a working hypothesis in these simple explanations of war. Granted the existence of groups formed by the accident of birth and based upon the most primitive protective and economic associations, and assuming the presence of the emotions of anger and fear or any instinct which is expressed as an impulse or habit of the group, we might say that the conditions and factors for the beginning of warfare are all present. When groups have desires that can best and most simply be satisfied by the exertion of force upon other groups, something equivalent to war has begun.