The hope had long persisted that this coastal plain might yield the ores, timber, ship stores and other products England needed, and for which she then largely depended on foreign potentates. Lacking an ample supply of cheap labor, however, colonial industries could not compete with well-established ones of the Old World. For well over a century tobacco proved the one commodity which the colony could profitably produce for the home market in large quantities. A notable result of the method of tobacco cultivation was a rapid depletion of the soil. Intent only upon reaping quick returns, men customarily neglected the most ordinary precautions to preserve fertility. Since the tobacco plant required the richest loam to produce the leaf in its perfection, fields were usually abandoned after three or more crops had been harvested, and "new grounds" were cleared. Thus there developed an ever recurring need for fresh lands. Under so wasteful a system, Virginians had soon realized the necessity of acquiring many times the quantity of land they could cultivate at any one time. Farseeing men, realizing a day would come when fertile soil could no longer be had for a song, wished also to provide sufficient elbow room for their children at a future day. The appreciation in land values in a new country provided a further incentive to the accumulation of large holdings. As a result, enterprising persons everywhere competed to secure the best tracts. Towards the close of the seventeenth century the practice of engrossing lands gained increased momentum. African slavery was rapidly superseding white indentured servitude as the principal source of labor supply. The price of tobacco had steadily declined owing to overproduction, the burdens of the Navigation Acts, and the effects of European wars. As a result of these conditions, the margin of profit from the leaf had so decreased that the cheaper labor of slaves and large-scale production had now become virtually essential to economic survival. After he had served his indentureship, the white servant could no longer establish himself as an independent farmer as he had once done, and the small yeoman now usually felt obliged to sell his lands to his wealthier neighbor and either become his tenant or migrate to some other section or colony. Political developments likewise favored the accumulation of large estates. Through repeated intermarriage certain families had acquired a very extensive influence. Members of these families were active in the Governor's Council or the House of Burgesses and held other high offices as a matter of course. Their official position often aided them as private individuals in acquiring lands. Through the presentation of "head right" certificates, compensation for military services, purchase from private proprietors, and other ways they obtained domains comprising thousands of acres. Some carved out what resembled small principalities.