The Wealth of Nations by Part 4 Chapter 1 Page 49

Few countries produce much more rude produce than what is sufficient for the subsistence of their own inhabitants. To send abroad any great quantity of it, therefore, would be to send abroad a part of the necessary subsistence of the people. It is otherwise with the exportation of manufactures. The maintenance of the people employed in them is kept at home, and only the surplus part of their work is exported. Mr. Hume frequently takes notice of the inability of the ancient kings of England to carry on, without interruption, any foreign war of long duration. The English, in those days, had nothing wherewithal to purchase the pay and provisions of their armies in foreign countries, but either the rude produce of the soil, of which no considerable part could be spared from the home consumption, or a few manufactures of the coarsest kind, of which, as well as