The Wealth of Nations by Part 4 Chapter 7 Page 114

In this respect, therefore, all the European colonies have, without exception, been a cause rather of weakness than of strength to their respective mother countries.

The colonies of Spain and Portugal only have contributed any revenue towards the defence of the mother country, or the support of her civil government. The taxes which have been levied upon those of other European nations, upon those of England in particular, have seldom been equal to the expense laid out upon them in time of peace, and never sufficient to defray that which they occasioned in time of war.

Such colonies, therefore, have been a source of expense and not of revenue to their respective mother countries.

The advantages of such colonies to their respective mother countries