Take, for example, the power over commerce.  According to the Constitution, the Federal Government had plenary power over foreign commerce and commerce between the States, but the power over commerce within a State was reserved to State governments.  This presupposed the power of Government to divide commerce into two water-tight compartments, or, at least, to regard the two spheres of power as parallel lines that would never meet; whereas with the coming of the railroad, steamship and the telegraph commerce has become so unified that the parallel lines have become lines of interlacing zigzags.  To adapt the commerce clause of the Constitution to these changed conditions has required, in the highest degree, the constructive genius of the Supreme Court of the United States, and, in a series of very remarkable decisions, which are contained in 256 volumes of the official reports, that great tribunal has tried to draw a line between inter-State and domestic commerce as nearly to the original plans of the framers as it was possible; but obviously there has been so much adaptation to make this possible that if Washington, Franklin, Madison and Hamilton could revisit the nation they created they would not recognize their own handiwork.

For the same reason, the dual system of government has been profoundly modified by the great elemental forces of our mechanical age, so that the scales, which try to hold in nice equipoise the Federal Government on the one hand and the States on the other, have been greatly disturbed.  Originally, the States were the powerful political entities, and the central government a mere agent for certain specific purposes; but, in the development of the Constitution, the nation has naturally become of overshadowing importance, while the States have relatively steadily diminished in power and prestige.

These inevitable tendencies in American politics are called “centralization,” and while for nearly a century a great political party bitterly contested its steady progress, due to the centripetal influences above indicated, yet the contest was long since abandoned as a hopeless one, and the struggle to-day is rather to keep, so far as possible, the inevitable tendency measurably in check.

Nevertheless, it would be erroneous to suggest that the dual system of government is a failure.  It still endures in providing a large measure of authority to the States in their purely domestic concerns, and, in a country that extends from the Atlantic to the Pacific, and from the Lakes to the Gulf, whose northern border is not very far from the Arctic Circle, and whose southern border is not many degrees from the Equator, there are such differences in the habits, conventions, and ideals of the people that without this dual form of government the Constitution would long since have broken down.  It is not too much to say that the success with which the framers of the Constitution reconciled national supremacy and efficiency with local self-government is one of the great achievements in the history of mankind.