In this supremacy of the national government within its proper sphere, and in the means which were devised for giving it practical efficiency, we are to look for the chief cause that has given to our system a capacity of great territorial extension. It is a system in which a few relations of the inhabitants of distinct States are confided to the care of a central authority; while, for the purpose of securing the uniform operation of certain principles of justice and equality throughout the land, particular restraints are imposed on the power of the States. With these exceptions, the several States remain free to pursue such systems of legislation as in their own judgment will best promote the interest and welfare of their inhabitants. Such a division of the political powers of society admits of the union of far greater numbers of people and communities, than could be provided for by a single representative government, or by any other system than a vigorous despotism. Many of the wisest of the statesmen of that period, as we now know, entertained serious doubts whether the country embraced by the thirteen original States would not be too large for the successful operation of a republican government, having even so few objects committed to it as were proposed to be given to the Constitution of the United States. If those objects had been made to embrace all the relations of social life, it is extremely probable that the original limits of the Union would have far exceeded the capacities of a republican and representative government, even if the first difficulties arising from the differences of manners, institutions, and local laws could have been overcome. But these very differences may be, and in fact have been, made a means of vast territorial expansion, by the aid of a principle which has been placed at the foundation of the American Union. Let a number of communities be united under a system which embraces the national relations of their inhabitants, and commits a limited number of the objects of legislation to the central organs of a national will, leaving their local and domestic concerns to separate and local authority, and the growth of such a nation may be limited only by its position on the surface of the earth. The ordinary obstacles arising from distance, and the physical features of the country, may be at once overcome for a large part of the purposes of government, by this division of its authority. The wants and interests of civilized life, modified into almost endless varieties, by climate, by geographical position, by national descent, by occupation, by hereditary customs, and by the accidental relations of different races, may in such a state of things be governed by legislation capable of exact adaptation to the facts with which it has to deal. In this way, separate States under the republican form may be multiplied indefinitely.