The wars of Charles XII, however, which proved disastrous to the Baltic trade, and the War of the Spanish Succession which cut off exports of tobacco to France and Spain, caused a serious decline in prices and made it impossible for the planters to continue the large purchases of slaves. This fact, together with the duty which had been imposed with the express purpose of keeping them out, reduced the importations to a minimum during the years from 1710 to 1718.[7-52] But with the reopening of the tobacco market and the return of prosperity to Virginia, the black stream set in again with redoubled force. In 1730, out of a total population of 114,000, no less than 30,000 were negroes.[7-53] In other words the slaves, who in 1670 had constituted but five per cent of the people, now comprised twenty-six per cent. Slavery, from being an insignificant factor in the economic life of the colony, had become the very foundation upon which it was established. As we have seen it was not slavery but the protracted accumulation of surplus stocks of tobacco in England which had broken the long continued deadlock of the tobacco trade during the Restoration period and caused the overflow into continental markets. That the labor of blacks at first played no essential part in the movement is evident from the fact that in 1682 when it first became pronounced, the slave population of Virginia and Maryland was still insignificant. But that the trade not only continued after the glut in England had been cleared up, but increased with startling rapidity, was unquestionably the result of more universal use of negroes in the years immediately preceding the War of the Spanish Succession. Slavery so cheapened the cost of production that it was now quite possible for those who used them to pay the half penny a pound duty on reëxported tobacco in England, and still undersell all rivals in the European market. Before many years had passed the tobacco trade, with all that it meant both to England and to the colonies, rested almost entirely upon the labor of the savage black man so recently brought from the African wilds.