The tribunals which act as umpires between the federal and the state governments naturally also decide all disputes between two states, or between a citizen of one state and the government of another. The usual remedies between nations, war and diplomacy, being precluded by the federal union, it is necessary that a judicial remedy should supply their place. The Supreme Court of the federation dispenses international law, and is the first great example of what is now one of the most prominent wants of civilized society, a real international tribunal. The powers of a federal government naturally extend not only to peace and war, and all questions which arise between the country and foreign governments, but to making any other arrangements which are, in the opinion of the states, necessary to their enjoyment of the full benefits of union. For example, it is a great advantage to them that their mutual commerce should be free, without the impediment of frontier duties and custom-houses. But this internal freedom can not exist if each state has the power of fixing the duties on interchange of commodities between itself and foreign countries, since every foreign product let in by one state would be let into all the rest; and hence all custom duties and trade regulations in the United States are made or repealed by the federal government exclusively. Again, it is a great convenience to the states to have but one coinage, and but one system of weights and measures, which can only be insured if the regulation of these matters is intrusted to the federal government. The certainty and celerity of post-office communication is impeded, and its expense increased, if a letter has to pass through half a dozen sets of public offices, subject to different supreme authorities: it is convenient, therefore, that all post-offices should be under the federal government; but on such questions the feelings of different communities are liable to be different. One of the American states, under the guidance of a man who has displayed powers as a speculative political thinker superior to any who has appeared in American politics since the authors of the "Federalist," [10] claimed a veto for each state on the custom laws of the federal Congress; and that statesman, in a posthumous work of great ability, which has been printed and widely circulated by the Legislature of South Carolina, vindicated this pretension on the general principle of limiting the tyranny of the majority, and protecting minorities by admitting them to a substantial participation in political power. One of the most disputed topics in American politics during the early part of this century was whether the power of the federal government ought to extend, and whether by the Constitution it did extend, to making roads and canals at the cost of the Union. It is only in transactions with foreign powers that the authority of the federal government is of necessity complete.