Slavery in the United States was a form of unfree labor which existed as a legal institution in North America for more than a century before the founding of the United States in 1776, and continued mostly in the South until the passage of the Thirteenth Amendment to the United States Constitution in 1865. The first English colony in North America, Virginia, first imported Africans in 1619, a practice established in the Spanish colonies as early as the 1560s. Most slaves were black and were held by whites, although some Native Americans and free blacks also held slaves; there were a small number of white slaves as well. Europeans also held some Native Americans as slaves, and African-Native Americans. Slavery spread to the areas where there was good-quality soil for large plantations of high-value cash crops, such as tobacco, cotton, sugar, and coffee. By the early decades of the nineteenth century, the majority of slaveholders and slaves were in the southern United States, where most slaves were engaged in a work-gang system of agriculture on large plantations, especially devoted to cotton and sugar cane. Such large groups of slaves were thought to work more efficiently if directed by a managerial class called overseers, usually white men.