As explained by James Mill in his Elements of Political Economy (2nd Edition, London: Baldwin, Cradock, and Joy, 1824, pp. 120 and 122):
“The benefit which is derived from exchanging one commodity for another, arises, in all cases, from the commodity received, not from the commodity given. When one country exchanges, in other words, when one country traffics with another, the whole if its advantage consists in the commodities imported. It benefits by importation, and by nothing else.
“This seems to be so very nearly a self-evident proposition, as to be hardly Continue reading
“When both countries can produce both commodities, it is not greater absolute, but greater relative, facility, that induces one of them to confine itself to the production of one of the commodities, and to import the other.
“When a country can either import a commodity, or produce it at home, it compares the cost of producing at home with the cost of procuring it from abroad; if the latter cost is less than the first, it imports.
“The cost at which a country can import from abroad depends, not upon the cost Continue reading
“The interest of the dealers, however, in any particular branch of trade or manufactures, is always in some respects different from, and even opposite to, that of the public. To widen the market and to narrow the competition, is always the interest of the dealers. To widen the market may frequently be agreeable enough to the interest of the public; but to narrow the competition must always be against it, and can serve only to enable the dealers, by raising their profits above what they naturally would be, to levy, for their own benefit, an absurd tax upon the rest of their fellow-citizens. The proposal of any new law or regulation of commerce which comes from this order, ought always to be listened to with great precaution, and ought never to be adopted till after having been long and carefully examined, not only with the most scrupulous, but with the most suspicious attention. It comes from an order of men, whose interest is never exactly the same with that of the public, who have generally an interest to deceive and even to oppress the public, and who accordingly have, upon many occasions, both deceived and oppressed it.”
— Adam Smith, The Wealth of Nations (1776).