This was but the beginning of the struggle, however. The Dutch resisted strenuously, stirring up the native chieftains against the English, seizing their vessels and breaking up their stations. Not until two wars had been fought was England able to wring from the stubborn Netherlanders an acknowledgment of her right to a share in the trade. Even then the Virginians were not adequately supplied, for the sugar islands were clamoring for slaves, and as they occupied so important a place in the colonial system they were the first to be served. Throughout the last quarter of the Seventeenth century negroes in fairly large numbers began to arrive in the Chesapeake, but it was only in the years from 1700 to 1720 that they actually accomplished the overthrow of the old system of labor and laid the foundations of a new social structure. Throughout the Seventeenth century the economic system of the tobacco colonies depended upon the labor of the poor white man, whether free or under terms of indenture; in the Eighteenth century it rested chiefly upon the black shoulders of the African slave. There could be no manner of doubt as to the desirability of the slaves from an economic standpoint, apparently the only standpoint that received serious consideration. The indentured servant could be held usually for but a few years. Hardly had he reached his greatest usefulness for his master than he demanded his freedom. Thus for the man of large means to keep his fields always in cultivation it was necessary constantly to renew his supply of laborers. If he required twenty hands, he must import each year some five or six servants, or run the risk of finding himself running behind. But the slave served for life. The planter who had purchased a full supply of negroes could feel that his labor problems were settled once and for all. Not only could he hold the slaves themselves for life, but their children also became his property and took their places in the tobacco fields as soon as they approached maturity.