powell] SOCIOLOGY, OA> THE SCIENCE OF INSTITUTIONS 707
construct a new communal dwelling for the joint use of the mem- bers of the clan. Thus the clan seems to be the most permanent and most fundamental unit in the organization.
In the study of North American tribes it is always found that the purpose assigned and recognized for the organization of that unit is the establishment of peace. Two or more bodies go to war, and finally agree to live in peace, and make a treaty; and the terms of the treaty are invariably of one character, if they unite as a tribe. This fundamental condition for the organiza- tion of a tribe is, that the one party agrees that its women shall be the wives of the other, with a reciprocal obligation. This is the characteristic which distinguishes tribes from confederacies. A body of people organized for the purpose of regulating mar- riage is a tribe. A body of people organized for war is a confederacy. Thus the organization of a tribe itself is the first recognition of the principle of peace in the origin of constitu- tions. The confederacy is always the unit of war organization. It is doubtful — in the present stage of investigation, at least — whether a tribe, as such, ever engages in offensive war. Con- federacies become tribes by customary intermarriages, especially when the tribe becomes the taboo unit of intermarriage. It is thus that the three units, the clan, the tribe, and the confederacy, are variable from time to time, although at any particular time these three units can be distinguished as well as the family or house- hold unit.
There are peculiar circumstances under which the household unit is variable. This variability depends upon customs which sometimes spring up among tribes, and are known as polyandry and polygamy. Sometimes the man who marries a woman is entitled to marry her sisters as they become of age. There are other conditions under which men become polygamists ; but they are not very common in savage society. In the same manner, there are cases in which the women of the clan are few as com- pared with the men to whom they are due ; and, hence, one
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