Such was the history of the Germanic invasions of Britain, the Scandinavian settlements on the shores of Iceland, Britain, and France, and the incursions of Saharan tribes into the Sudanese states.

Among pastoral nomads war is the rule; the tribe, a mobilized nation, is always on a war footing with its neighbors.

The scant supply of wells and pasturage, inadequate in the dry season, involves rivalry and conflict for their possession as agricultural lands do not.

Failure of water or grass is followed by the decline of the herds, and then by marauding expeditions into the river valleys to supply the temporary want of food.

When population increases beyond the limits of subsistence in the needy steppes, such raids become the rule and end in the conquest of the more favored lands, with resulting amalgamation of race and culture.[154] [Sidenote: Primitive war.] The wars of savage and pastoral peoples affect the whole tribe.