I94 AFRICAN POLITICAL SYSTEMS
dependence on economic factors and, tied up with them, environmental conditions. The impetus to colonization and expansion, as we saw it, was already implied in the way in which the people gain their livelihood. We can render this argument even more conclusive; the cultural situation in the river valley itself offers us the comparative material from which to draw our deductions. We remember the upper-stream Kede, who, neighbours, fellow tribesmen and in many details of culture close relations of the down-stream Kede, yet do not share their political achievements— and also do not share their productive system and economic life in general. We can even go further and point to the environmental factors on which the economic system of the Kede in turn depends. The environment in which the upper-stream Kede live indeed forbids a development of river trade and traffic similar to that evolved by the sister group. The river in their area is narrow, barred in several places by rapids and rocky, frequently dangerous, passages, and generally impassable during half the year. On its banks there are few settlements, and the hinterland is thinly populated, inhabited largely by comparatively poor and backward groups. Hold against this the down-stream country: a broad river, navigable all the year round, the banks covered with numerous villages and the hinterland a rich, populous country with highly developed trades and crafts.
It will have been seen that I am speaking here of environment in a rather wide sense, including, beside the physical constellation of the country, also such factors as distribution of population and the existence of a certain type of civilization. Methodologically, these facts stand in the same category as physical environment proper. True, they are essentially historical facts, representing the results of various historical developments. These developments themselves, however, are beyond our line of vision; their results—the fact that the Kede area happens to lie in the centre of a rich and powerful kingdom—are to us 'unique events' in the phraseology of the historian, extraneous factors of chance, which, like environmental facts, we have to accept as ultimate data.
Let me admit that this causal chain, environmental conditions— economic enterprise—political system, is not fully conclusive. It is weakened by another aspect of our comparative evidence— namely, the fact that the kintsoji, who are also close neighbours and tribal relations of the down-stream Kede, and who share with