Before leaving the statistics of the growth of cities, it is worth our while to note that certain great urban centers are developing in this country which promise to show, even in the near future, the most extensive urbanization of population known to the world; for example, a line of cities and suburban communities is now developing which will in the near future connect New York and Boston on the one hand and New York, Philadelphia, and Washington on the other hand. Thus in a few years, stretching from Washington to Boston, a distance of five hundred miles, there promises to be a continuous chain of urban communities with practically no rural districts between them. In a sense, this will constitute one great city with a population of twenty millions or upwards. Other urban centers, though not so extensive, are also developing at other points in the United States. At the end of the twentieth century it is safe to say that this country will have at least a dozen cities with a population of over one million. Moreover, so far as we can see at the present time, there is no end in the near future to this growth of the urbanization of our population; for the causes of this great growth of cities seem inherent in our civilization. Let us see what these causes are. Causes of the Growth of Great Cities.--There may be distinguished two classes of causes of the growth of cities: (1) general or social causes, and (2) minor or individual causes. It is the social causes, the causes inherent in our civilization, which are of particular interest to us. Among these social causes we shall place: 1. _The Diminishing Importance of Agriculture in the Life of Man._ Once agriculture was the all-embracing occupation. Practically all goods were produced upon the farm. Now, however, man's wants have so greatly increased that the primitive industries of the farm can no longer satisfy these wants, and in order to satisfy them men have developed large manufacturing industries. Moreover, fewer men are needed on the farms to produce the same amount of raw material as was produced formerly by the labor of many. This has come about mostly through labor-saving machines. The invention and application of labor-saving machines to the industries of the farm has made it possible to dispense with a great number of men. It is estimated that fifty men with modern farm machinery can do the work of five hundred European peasants without such machinery. Consequently, the four hundred and fifty who have been displaced by farm machinery must find other work, and they find it mainly in manufacturing industries. Again, the scientific and capitalistic agriculture of the present has much the same effect as labor-saving machines. They have greatly increased agricultural production and at the same time lessened the amount of labor. The opening up also of new and fertile regions which were very productive in the nineteenth century had a similar effect.