Interference with free trade with the foreigner has always been in large measure due to political motives. In every petty medieval state or self-governing city, the aim was to make the economic boundaries coincide as nearly as possible with the political boundaries. Except for the trade in a few articles of comparative luxury this aim was at that time nearly attainable. The peasantry surrounding a fortified town and enjoying its protection were compelled to trade there. Down to our own time it has seemed to statesmen expedient to forbid or discourage trade that might nourish the economic power of future enemies. Sometimes governments have used embargoes, bounties, or tariffs as weapons to injure the trade of other nations and to secure diplomatic or commercial concessions. Often they have sought by tariffs to encourage the building of ships and the manufacture of armaments and of all kinds of munitions by private enterprise within their own borders, even when the immediate cost of these products was greater than if they were purchased abroad. In such cases it is always a question whether an outright expenditure would not be better, whether the government could not build its own arsenals and shipyards more economically than it can foster private enterprise by means of a protective tariff. However, the political (or military) argument for protection recognizes that it is in itself a costly (not a profitable) policy, and that the cost is only justified on the grounds that military necessity warrants the outlay. The military argument as applied to the preparation of ships and munitions has no application to a tariff on those articles which have no bearing upon military power. But the most recent application of science and the mechanical arts to the uses of war has given new significance to a larger policy of industrial preparedness for military purposes. The year 1914 doubtless ushered in for the world a new epoch of protective and discriminatory tariff legislation determined by political rather than by direct economic considerations.