ory factor to a movement. The
economic causes are by far the most important and universal; but
behind them are frequently other causes. "Political maladjustments
often express themselves through economic or social disabilities,
religious differences through economic and social limitations, etc."
In short, it may be said that the motives of migration may be due to a
complication of causes. This may be well illustrated by the study of
the recent Negro migration in which it will be found that this
movement was occasioned by a number of interacting economic, social,
and, to a small extent, political forces.

As there are types of forces or causes giving rise to migration, there
are likewise types of migration. These are the following four:
invasion, conquest, colonization and immigration. Besides these four
main types of movement there are other less important forms which
deserve notice. They are of two kinds, namely, forced forms of
migration, and internal or intra-state migration of peoples. The
former occurs (1) when people are expelled from a country because of
non-conformity to the established religion; (2) when they are
compelled by actual force to leave one place and go to another, as in
the case of the importation of Negroes from Africa to the United
States to become slaves; and (3) when people are subjected to
banishment from a country as a form of punishment for crime. The
internal or intra-state movement is that which is going on all the
time in most civilized countries, and which is usually a phenomenon of
non-importance; but when it involves large masses of people, moving in
certain well-defined directions, with a community of motives and
purposes, it becomes of great interest and significance and deserves
to be classed with the other great movements of peoples. One good
example of this is the westward movement of the people of the United
States during the early decades of the past century. Another which
might be rightly classed as such is the recent large Negro migration
which is under consideration in this essay.

The subject of migration in general is capable of very lengthy
treatment, but as this is not our purpose here we shall terminate this
discussion at this juncture. In this preliminary survey the aim has
been to try to show, though in an exceedingly brief manner, the
meaning and significance of migration as a factor in the human
struggle for existence; the distinction between migration and the
earl