§ 4. #Persistence of difference between nations#. If both men and wealth interchanged between industries and between countries with perfect readiness and without any outlay whatever for transportation, these differences would soon disappear, and perfect equilibrium of advantage would everywhere result. In every country, in every occupation, labor and wealth of given quality and amount would receive the same reward. But the interchange of labor and of products between countries is never without friction. The laborers, enterprisers, and investors in a naturally rich country are thus in a position of more or less enduring advantage relative to those of older and poorer countries. Differences of the same nature appear as between different parts of the same country, as between the Northern and the Southern states of the American union, between the Eastern and the Western states, and even between neighboring countries of the same state. The differences between two countries, however, are likely to be more marked, the circulation of factors being so active within a country that it is allowable to speak broadly of prevailing national rates of wages and of interest. Altho, as Adam Smith said, "a man is of all sorts of luggage the most difficult to be transported," the higher wages in a new country attract constantly from the older lands a portion of their laborers. The higher rate of interest in new countries constantly attracts investments from abroad; yet, despite these forces working toward equalization, the inequality may remain and, through the working of other influences, may even increase in the course of years. § 5. #Doctrine of comparative advantages.# It may be that two countries both possess the necessary technical conditions for making both articles that are to be traded for each other. It may even be that the people in one country would be able to make not only one of the two objects of trade, but both of them, more easily and with less sacrifice and effort than the people in the other. If, for example, American labor can produce two bushels of wheat in a day and English labor but one bushel a day; and American labor can produce just as much iron in a day as English labor--or more--the question always arises: Is it not foolish and wasteful not to produce both the wheat and the iron? Now, exactly the same case is presented in almost every simple neighborhood trade. The proprietor may be able to keep his books better than does the bookkeeper whom he employs. The merchant may be able to sweep out the store better than the cheap boy does it. The carpenter may be able to raise better vegetables than can the gardener from whom he purchases. Yet the merchant does not turn to sweeping and the carpenter to raising vegetables, because if they did they would have to quit or limit by so much their present better-paying work, and would lose far more than they would gain.