Of these three factors any one alone would be a powerful stimulus to trade; the three working together account for the astounding growth of commerce during the nineteenth century. Comparing the present and earlier periods we may characterize the advance by saying that in the Middle Ages commerce concerned itself almost entirely with the luxuries of life; that in the modern period (1500-1800) it served mainly men’s comfort; while in the recent period, since 1800, it has become necessary to the very existence of a considerable part of mankind. =372. Growth of the sphere of commerce and resulting specialization of production.=—The world has gone far toward realizing the ideal of the early free trader, that wherever a man might be, he should share in the productive advantages of all other men, wherever they might be. Customs tariffs have been able to check the movement of commerce; they have been powerless to stop it. The sphere of ordinary trade, which was once the manor, a mere hamlet or village; which grew in time to be the town with its surrounding country; then included the whole nation; and became in the modern period international,—this sphere of regular and ordinary trade is now the world. Whole countries now specialize in the production of different articles, as individuals or small districts once did. Northwestern Europe has become a great factory, drawing its food supplies and raw materials from distant parts of the world, and exporting manufactured products in exchange. Beside Europe stands the continent of North America, supplying in large part the needs of its own people for manufactures, and producing a surplus for export. North America, indeed, stands in one aspect above Europe, for it has unexhausted stores of natural resources which it lavishes on other parts of the world less richly endowed. The other continents take subordinate positions. They are enabled by commerce to procure from Europe and North America the manufactured goods which they require, and specialize in the production of various food supplies and raw materials for the means of purchasing these goods. =373. Abolition of the slave trade.=—The description of the present world-organization of production, and of the exchange of wares to which it gives rise, belongs to the department of commercial geography. It is proper here, however, to call attention to some of the marked changes in the wares of trade which have taken place since 1800. One ware which was, before 1800, of great commercial importance, and which yielded immense profits to those who dealt in it, has disappeared with the abolition of the slave trade by all civilized nations. Long before the abolition of slavery itself, humanity revolted against the horrors of the “middle passage,” and the protests took effective form about 1800; the states of Europe and America agreed, one after another, that the slave-trade under their flags, and for the supply of their territories, should cease.