The Wealth of Nations by Part 1 Chapter 11 Page 171

Portugal, however, is but a very small part of Europe, and the declension of Spain is not, perhaps, so great as is commonly imagined. In the beginning of the sixteenth century, Spain was a very poor country, even in comparison with France, which has been so much improved since that time. It was the well known remark of the Emperor Charles V, who had travelled so frequently through both countries, that everything abounded in France, but that everything was wanting in Spain. The increasing produce of the agriculture and manufactures of Europe must necessarily have required a gradual increase in the quantity of silver coin to circulate it; and the increasing number of wealthy individuals must have required the like increase in the quantity of their plate and other ornaments of silver.

Secondly, America is itself a new market