sentences:  Towards the end of the 17th century, English policy shifted in favor of retaining cheap labor rather than shipping it to the colonies, and the supply of indentured servants in Virginia began to dry up; by 1715, annual immigration was in the hundreds, compared with 1,500–2,000 in the 1680s.As tobacco planters put more land under cultivation, they made up the shortfall in labor with increasing numbers of slaves.The institution was rooted in race with the Virginia Slave Codes of 1705, and from around 1710 the growth in the slave population was fueled by natural increase.