During the mercantilist era it was often suggested, if not actually believed, that the principal benefit of foreign trade was the importation of gold and silver. According to this view the benefits to one nation were matched by costs to the other nations that exported gold and silver, and there were no net gains from trade. For nations almost constantly on the verge of war, draining one another of valuable gold and silver was thought to be almost as desirable as the direct benefits of trade. Adam Smith refuted the idea that the wealth of a nation is measured by the size of the treasury in his famous treatise The Wealth of Nations, a book considered to be the foundation of modern economic theory. Smith made a number of important criticisms of mercantilist doctrine. First, he demonstrated that trade, when freely initiated, benefits both parties. Second, he argued that specialization in production allows for economies of scale, which improves efficiency and growth. Finally, Smith argued that the collusive relationship between government and industry was harmful to the general population. While the mercantilist policies were designed to benefit the government and the commercial class, the doctrines of laissez-faire, or free markets, which originated with Smith, interpreted economic welfare in a far wider sense of encompassing the entire population.