This does not mean that any man will necessarily act in the same way to-morrow as he did yesterday, when subjected to the influence of the same threat, inducement, or temptation; because, without grappling the thorny question of free will, we realize that a man's action is never the result of only one stimulus and motive, but is the resultant of many; and we have no reason to expect that he will act in the same way when subjected to the same stimulus, unless we know that the internal and external conditions pertaining to him are also the same. Furthermore, even if we cannot predict what a certain individual will do, when exposed to a certain external influence, because of some differences in his mental and physical condition, on one occasion in comparison with another, yet when we consider large groups of men, we know that individual peculiarities, permanent and temporary, balance each other in great measure; that the average condition of a group of men is less changeable than that of one man, and that the degree of permanency of condition increases with the number of men in the group. From this we may reasonably conclude that, if we know the character of a man--or a group of men--and if we know also the line of action which he--or they-have followed in the past, we shall be able to predict his--or their--line of action in the future with considerable accuracy; and that the accuracy will increase with the number of men in the group, and the length of time during which they have followed the known line of action. Le Bon says: "Every race carries in its mental constitution the laws of its destiny." Therefore, the line of action that the entire human race has followed during the centuries of the past is a good index--or at least the best index that we have--to its line of action during the centuries of the future. Now, men have been on this earth for many years; and history and psychology teach us that in their intercourse with each other, their conduct has been caused by a combination of many forces, among which are certain powerful forces that tend to create strife. The strongest by far of these forces is the _ego_ in man himself, a quality divinely implanted which makes a man in a measure self-protecting. This ego prompts a man not only to seek pleasure and avoid trouble for himself, but also to gain superiority, and, if possible, the mastery over his fellow men. Men being placed in life in close juxtaposition to each other, the struggles of each man to advance his own interests produce rivalries, jealousies, and conflicts. Similarly with nations. Nations have been composed for the most part of people having an heredity more or less common to them all, so that they are bound together as great clans. From this it has resulted that nations have been jealous of each other and have combated each other. They have been doing this since history began, and are doing it as much as ever now.