The results of the first Part will be utilized in this. We have seen that slavery exists or formerly existed among many savage tribes, whereas many others have always, as far as we know, been unacquainted with it. The present Part will be taken up with an inquiry into the causes of these phenomena. We shall try to find out, what kinds of tribes have slaves, and what kinds have not.

Having now determined what is the meaning of the term „slavery”, we are about to inquire, what is its social signification, what place does it occupy in those societies where it formerly existed or still exists? But then we must first know, whether slavery exists among all savage tribes, and, if not, whether it is confined to certain races of men or to certain parts of the world; and further, whether it is found on all levels of lower culture, or on some only, and if the latter, on which. The solution of these problems requires a survey of the occurrence of slavery among wild tribes in the several parts of the globe. This survey will occupy the present chapter.

In most branches of knowledge the phenomena the man of science has to deal with have their technical names; and, when using a scientific term, he need not have regard to the meaning this term conveys in ordinary language; he knows he will not be misunderstood by his fellow-scientists. For instance, the Germans call a whale Wallfisch, and the English speak of shell-fish; but a zoölogist, using the word fish, need not fear that any competent person will think he means whales or shell-fish.

The causes which lead to the keeping of slaves, and those which prevent it, have been divided by us into internal and external causes. These terms do not perhaps quite answer the purpose, but we cannot find other terms which would express our meaning better, without requiring a prolix circumlocution. We think, however, that it is clear what we mean by these terms. Slavery cannot exist, where there are no internal causes requiring it, i. e. where there is no use, economic or non-eco-mic, for slave labour. A tribe will not keep slaves, even though its coercive power would enable it to do so, if there is no employment for them; in such case positive internal causes fail. The same obtains, where negative internal causes are found, i. e. where there are definite circumstances which make slave labour useless. The positive internal causes may also be called motive-forces. Slaves will not be kept, even where the best opportunities of procuring them exist, if there is no motive-force which requires the keeping of slaves, i. e. if they are not wanted.