Systematic study for an understanding of the laws of political  economy is to be found no farther back than the sixteenth century. The history of political economy is not the history of economic institutions, any more than the history of mathematics is the history of every object possessing length, breadth, and thickness.
Economic history is the story of the gradual evolution in the thought of men of an understanding of the laws which to-day constitute the science we are studying. It is essentially modern.1 Aristotle2 and Xenophon had some comprehension of the theory of money, and Plato3 had defined its functions with some accuracy.
The economic laws of the Romans were all summed up in the idea of enriching the metropolis at the expense of the dependencies. During the middle ages no systematic study was undertaken, and the nature of economic laws was not even suspected. It is worth notice that the first glimmerings of political economy came to be seen through the discussions on money, and the extraordinary movements of gold and silver. About the time of Charles V, the young study was born, accompanied by the revival of learning, the Reformation, the discovery of America, and the great fall in the value of gold and silver. Modern society was just beginning, and had already brought manufactures into existence—woolens in England, silks in France, Genoa, and Florence; Venice had become the great commercial city of the world; the Hanseatic League was carrying goods from the Mediterranean to the Baltic; and the Jews of Lombardy had by that time brought into use the bill of exchange. While the supply of the precious metals had been tolerably constant hitherto, the steady increase of business brought about a fall of prices. From the middle of the fourteenth to the end of the fifteenth century the purchasing power of money increased in the ratio of four  to ten.
Then into this situation came the great influx of gold and silver from the New World. Prices rose unequally; the trading and manufacturing classes were flourishing, while others were depressed. In the sixteenth century the price of wheat tripled, but wages only doubled; the laboring-classes of England deteriorated, while others were enriched, producing profound social changes and the well-known flood of pauperism, together with the rise of the mercantile classes. Then new channels of trade were opened to the East and West. Of course, men saw but dimly the operation of these economic causes; although the books now began to hint at the right understanding of the movements and the true laws of money.
The prohibition of the export of coin was embarrassing to the East India Company and to merchants; and Mun tried to show that freedom of exportation would increase the amount of gold and silver in a country, since the profits in foreign trade would bring back more than went out. It probably was not clear to them, however, that the export of bullion to the East was advantageous, because the commodities brought back in return were more valuable in England than the precious metals. The purpose of the mercantilists was to increase the amount of gold and silver in the country. Mun, with some penetration, had even pointed out that too much money was an evil; but in 1663 the English Parliament removed the restriction on the exportation of coin.  The balance-of-trade heresy, that exports should always exceed imports (as if merchants would send out goods which, when paid for in commodities, should be returned in a form of less value than those sent out!), was the outcome of the mercantile system, and it has continued in the minds of many men to this day. The policy which aimed at securing a favorable balance of trade, and the plan of protecting home industries, had the same origin. If all consumable goods were produced at home, and none imported, that would increase exports, and bring more gold and silver into the country. As all the countries of Europe had adopted the mercantile theory after 1664, retaliatory and prohibitory tariffs were set up against each other by England, France, Holland, and Germany.
A natural consequence of the navigation acts, and of the mercantile system, was the so-called colonial policy, by which the colonies were excluded from all trade except with the mothercountry. A plantation like New England, which produced commodities in competition with England, was looked upon with disfavor for her enterprise; and all this because of the fallacy, at the foundation of the mercantile system, that the gain in international trade is not mutual, but that what one country gains another must lose.
A connected and comprehensive grasp of principles was the great achievement of Adam Smith;28 for, although the “Wealth of Nations” was naturally not without faults, it has been the basis of all subsequent discussion and advance in political economy. In Books I and II his own system is elucidated, while Book IV contains his discussion of the Agricultural School and the attacks on the mercantile system. Seeing distinctly that labor was the basis of all production (not merely in agriculture), he shows (Books I and II) that the wealth of a country depends on the skill with which its labor is applied, and upon the proportion of productive to unproductive laborers.
The gains from division of labor are explained, and money appears as a necessary instrument after society has reached such a division. He is then led to discuss prices (market price) and value; and, since from the price a distribution takes place among the factors of production, he is brought to wages, profit, and rent. The  functions of capital are explained in general; the separation of fixed from circulating capital is made; and he discusses the influence of capital on the distribution of productive and unproductive labor; the accumulation of capital, money, paper money, and interest.