It may be well, also, to distinguish between the causes and motives of migration. Motives are subjective feelings existing within the individual which inspire his actions. They are the immediate forces which lead to movement, and may be divided into the same two general classes as causes. Causes are objective forces or conditions existing outside of the individual, which react upon him. They may exist in the physical environment or in the human environment, and operate by arousing motives, which in turn are the immediate springs of conduct. Since human nature is everywhere enough alike so that similar causes arouse similar motives, and since motives can hardly arise without some exterior cause, in our search for the origins of migratory movements it will ordinarily be sufficient to examine merely the causes. Thus in almost every case of migration we are justified in looking for some cause of a repellent nature, some dissatisfaction, disability, discontent, hardship, or other disturbing condition.[[3]]
These discomforts may arise in any of the various interests of human life, and may be classified according to almost any classification which will include those interests. Probably the most satisfactory is the familiar one of Economic, Political, Social, and Religious. The economic causes of migrations are the earliest and by far the most important. They arise in connection with man’s efforts to make his living, and concern all interests which are connected with his productive efforts. They are disabilities or handicaps which affect his pursuit of food, clothing, and shelter, as well as the less necessary comforts of life. These are vital interests, and any dissatisfaction connected with them is of great weight with men.
There is a wide variety of economic causes of migration, of which the following may be noted. Permanent natural inhospitableness of soil or climate or scarcity of natural resources may make the struggle for existence a perpetually hard one. Temporary natural calamities, such as drought, famine, flood, extreme seasons, etc., may interrupt the course of an ordinarily tolerable existence. Serious underdevelopment of the industrial arts may make life difficult in a nation by limiting the productive power of its citizens or handicapping them in the struggle for trade. A common economic cause of migration is overpopulation. This means that the population of a region has increased to the point where, under the existing industrial conditions, there are too many people for the supporting power of the soil. In man’s struggle with nature for a time an increase in numbers is an advantage. But there comes a point where the ratio between men and land reaches such an equilibrium that any increase in the number of men means a smaller amount of the materials of existence for each one.[[4]] This results in hardship and dissatisfaction. Many migratory movements, particularly in the case of primitive men, or men on a low stage of culture, may be very simply explained by overpopulation.
Political causes are those connected with the organization of government or the actions of the governing power. In this case the dissatisfaction arises from the failure of the individual or group to secure what is believed to be a rightful share in the control of the government, or in some positive repressive or persecuting measures on the part of the governing body toward some of its citizens. Hence we may look for motives of infringed liberty, lack of freedom, or the feeling of oppression. A bad government may put such handicaps on the entire body of its citizens as to make life unsatisfactory to them.
Where social causes of migration exist, the dissatisfaction arises from some fault in the social organization. Some classes or individuals are subjected to a feeling of inferiority to other classes or individuals. A caste, or aristocratic, organization of society gives certain classes an advantage over others, and makes it impossible for the lower classes to rise to a higher level. In case people living under these conditions learn of another region where advancement is possible, migration may easily ensue.
Religious causes include those cases where restrictions are placed on certain members of the body politic because of their religious beliefs or practices. There may be actual persecution, though this is coming to be somewhat rare in modern times. The oppression may manifest itself in various disadvantages, imposed on other interests of life, but which are primarily due to religious differences. The great historical example of this class of causes is found in the case of the Jews.
All of these kinds of causes may overlap, and almost always two or more of them exist in conjunction. Cases where social causes alone account for a migration are rare. They are frequently, however, a contributory factor. The economic causes are by far the most important and universal, though we need frequently to look for other causes back of them. Political maladjustments often express themselves through economic or social disabilities, religious differences through economic and social limitations, etc. In any actual case of migration it is probable that the motives of migration will be due to a complication of causes. This fourfold classification, however, is of great aid in isolating and understanding the underlying forces.
The effects of migratory movements, involving the transference of bodies of people from one region to another, are far-reaching and extremely diversified. They concern both the country of origin and the country of destination. They differ widely in specific cases, so much so that it is scarcely possible to lay down any general rules or conclusions which will be of value. They manifest themselves under three main heads, viz. the density of population, the physical stock, and the customs and institutions, or mores. The most obvious effect, and the one which is commonly assumed to follow any migration, is a decrease in the population of the country of source, and an increase in that of the country of destination. But even this, as will appear hereafter, is not by any means the universal rule. There is commonly some effect on the physical stock of the country receiving the migrants. This effect may vary between wide extremes. Whether the customs and institutions shall be also affected depends upon a variety of circumstances which are likely to make each instance distinctive. There is scarcely one of the vital interests of either country concerned which may not be deeply affected by an important migratory movement. But the factors concerned are so complicated, and so subject to individual variation, that movements which bear a general resemblance may have very diverse effects, and each case must be studied by itself.
As to the routes or channels of migratory movements, it may be said that in general they follow the lines of least resistance, as determined by the combination of all the forces involved. The closer the movement is to a purely natural one, the more it will follow the natural routes marked out by the configuration of the earth. River valleys, such as the Danube in Europe and the Ohio in America, have always been favorite migratory routes. If mountains have to be traversed, the easiest passes will be chosen, such as the Cumberland Gap in the United States. In general, water has been a bond and not a barrier between different lands, and the earliest routes of distant travel were undoubtedly by water. Greece became the source of numerous migratory movements partly because of her extended coast line.[[5]]
Having thus considered some of the essential features of migration as a whole, it will be well to distinguish further between the four great types of migrations to which reference has been made. One of the earliest, simplest, and most natural of migratory movements is the invasion. This occurs when a rude people, on a low stage of culture, but with much native physical virility, leaves its location, and overruns the territory of a more highly developed state. It is a movement en masse, involving the whole, or a large portion, of the tribe. The tribe acts as a unit, and the end sought is the benefit of the tribe as a tribe, not of any individuals. The forces back of it approach the unconscious and irrational, characteristic of wandering, more closely than in any other form of migration.