Manifestly the extension of agriculture and industry in so large a country as the United States was dependent upon the corresponding growth of the means of transportation, both by water and by rail. A detailed account of the expansion of the railway net, with the accompanying' implications in the fields of finance and politics, is a matter for later consideration. Certain of its general features may be mentioned, however, because they are intimately interwoven with the economic developments which have just been explained. The concentration of the population in the cities, of which New York and Chicago were outstanding examples, was one of these features. From the time of the first census, the city of New York continued to maintain its position as the most populous city of the nation. Between 1850 and 1890 it added a round million to its numbers, containing 1,515,000 persons at the later date. Moreover it was the center of a thriving and thickly settled region extending from New Haven on the one side to Philadelphia on the other--the most densely populated area in America. The uninterrupted expansion of the city indicated that the reasons for its growth were constant in their operation. And, in fact, the reasons were not difficult to find. It was blessed with one of the world's finest harbors and had access to the interior of the state by way of the Hudson and Mohawk rivers. These natural advantages had long since been recognized and had been increased by the construction of the Erie Canal in 1825 which, with the Great Lakes and the several canals connecting the Lakes with the Ohio Valley, had given New York an early hold and almost a monopoly on the trade between the upper Mississippi, the Lakes and the coast. The city, therefore, became an importing and exporting center; its shipping interests grew, immigration flowed in, and its manufacturing establishments soon outstripped those of any other industrial center; the great printing and publishing, banking and commercial firms were drawn irresistibly to the most populous city, and Wall Street became the synonym for the financial center of the nation.