Another American plant has had an important influence on the history of American commerce, though it did not aid in the settlement of the country,—tobacco. That singular gift of the New World to the Old quickly gave the basis of a great export to the colonies of Maryland, Virginia, and North Carolina; it alone enabled the agriculture of the Southern colonies to outgrow in wealth those which were planted in more northern soil. To this crop, which demands much manual labor of an unskilled kind, and rewards it well, we owe the rapid development of African slavery. It is doubtful if this system of slavery would ever have flourished if America had been limited in its crops to those plants which the settlers brought from the Old World. Although African slavery existed for a time in the States north of the tobacco region, it died away in them even before the humanitarian sentiments of modern times could have aided in its destruction; it was the profitable nature of tobacco crops which fixed this institution on our soil, as it was the great extension of cotton culture which made this system take on its overpowering growth during the first decades of the nineteenth century. Another interesting effect of the conditions of tillage which met the early settlers upon this soil depends upon the peculiar distribution of forests in North America. All those regions which were first occupied by European peoples were covered by very dense forests. To clear these woods away required not less than thirty days’ labor to each acre of land. In the glaciated districts, as before remarked, this labor of preparation was nearly doubled. The result was that the area of tillage only slowly expanded as the population grew denser, and the surplusage of grain for export was small during the first two centuries. When in the nineteenth century the progress westward suddenly brought the people upon the open lands of the prairies, the extension of tillage went on with far greater celerity. We are now in the midst of the great revolution that these easily won and very fertile lands are making in the affairs of the world. For the first time in human history, a highly skilled people have suddenly come into possession of a vast and fertile area which stands ready for tillage without the labor that is necessary to prepare forest lands for the plough. They are thus able to flood the grain-markets of the world with food derived from lands which represent no other labor beyond tillage except that involved in constructing railways for the exportation of their products. This enables the people of the Western plains to compete with countries where the land represents a great expenditure of labor in overcoming the natural barriers to the cultivation of the soil.