In earlier conditions of life, population was kept down to the community balance by variations in the death-rate, or, as in the case of Greek cities, the surplus population emigrated in groups to establish new colonies—offshoots of the mother-city. Under modern conditions of communication and transportation, population adjustment is maintained by a ceaseless process of individual migrations. As a result of the dynamic conditions prevailing throughout the civilized world during the last fifty years, many communities have passed through swift successive cycles of growth or decline, the determining factors being changes in forms and routes of transportation and communication and the rise of new industries. Some advantage in transportation is the most fundamental and most important of the causes determining the location of a distributing center. It may almost be said to be the only cause for the formation of such centers. For some reason or reasons a particular place is more conveniently and cheaply reached by many people than any surrounding point; and, as a result, they naturally exchange commodities there. The country store is located at the crossing of roads. There also is the village. In a mountain country the market town is at the junction of two, or, still better, of three valleys. Another favorite location is the end of a mountain pass, or a gap that is a thoroughfare between two valleys. If rivers are difficult to cross, settlements will spring up at the safest ferries or fords. In a level plain, a town will be near its center, and a focus of roads or railroads in such a plain, fertile and populous, will almost surely make a city.[42] It is the railroad and the steamship that determine where a new business shall be developed, quite as often as the government policy. The grant of special rates and privileges to shippers is nowadays the most efficient kind of protection. It is this quickening and cheapening of transportation that has given such stimulus in the present day to the growth of large cities. It enables them to draw cheap food from a far larger territory and it causes business to locate where the widest business connection is to be had, rather than where the goods or raw materials are most easily produced. And the perfection of the means of communication, the post-office and the telegraph, intensifies the same result.[43] The entire net increase of the population of 1870 to 1890 in Illinois, Wisconsin, Iowa, and Minnesota was in cities and towns possessing competitive rates, while those having non-competitive rates decreased in population, and in Iowa it is the general belief that the absence of large cities is due to the earlier policy of the railways giving Chicago discriminating rates.[44]