The Wealth of Nations by Part 4 Chapter 7 Page 158

great, though distant, market for such parts of the produce of British industry as may exceed the demand of the markets nearer home, of those of Europe, and of the countries which lie round the Mediterranean Sea. In its natural and free state, the colony trade, without drawing from those markets any part of the produce which had ever been sent to them, encourages Great Britain to increase the surplus continually by continually presenting new equivalents to be exchanged for it. In its natural and free state, the colony trade tends to increase the quantity of productive labour in Great Britain, but without altering in any respect the direction of that which had been employed there before. In the natural and free state of the colony trade, the competition of all other nations would hinder the rate of profit from rising above the common level either in the new market or in the new employment.