reconstruct its past, shows incessant movement,—­growth, expansion and short-lived conquest, followed by shrinkage, expulsion or absorption by another invader.[127] To this constant shifting of races and peoples the name of historical movement has been given, because it underlies most of written history, and constitutes the major part of unwritten history, especially that of savage and nomadic tribes.  Two things are vital in the history of every people, its ethnic composition and the wars it wages in defense or extension of its boundaries.  Both rest upon historical movements,—­intrusions, whether peaceful or hostile, into its own land, and encroachments upon neighboring territory necessitated by growth.  Back of all such movements is natural increase of population beyond local means of subsistence, and the development of the war spirit in the effort to secure more abundant subsistence either by raid or conquest of territory.

[Sidenote:  Evolution of the Historical Movement.]

Among primitive peoples this movement is simple and monotonous.  It involves all members of the tribe, either in pursuit of game, or following the herd over the tribal territory, or in migrations seeking more and better land.  Among civilized peoples it assumes various forms, and especially is differentiated for different members of the social group.  The civilized state develops specialized frontiersmen, armies, explorers, maritime traders, colonists, and missionaries, who keep a part of the people constantly moving and directing external expansion, while the mass of the population converts the force once expended in the migrant food-quest into internal activity.  Here we come upon a paradox.  The nation as a whole, with the development of sedentary life, increases its population and therewith its need for external movements; it widens its national area and its circle of contact with other lands, enlarges its geographical horizon, and improves its internal communication over a growing territory; it evolves a greater mobility within and without, which attaches, however, to certain classes of society, not to the entire social group.  This mobility becomes the outward expression of a whole complex of economic wants, intellectual needs, and political ambitions.  It is embodied in the conquests which build up empires, in the colonization which develops new lands, in the world-wide exchange of commodities and ideas which lifts the level of civilization, till this movement of peoples becomes a fundamental fact of history.

[Sidenote:  Nature of primitive movements.]