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.