Slavery in the colonial history of the United States, from 1526 to 1776, developed from complex factors, and researchers have proposed several theories to explain the development of the institution of slavery and of the slave trade. Slavery strongly correlated with the European colonies' demand for labor, especially for the labor-intensive plantation economies of the sugar colonies in the Caribbean and South America, operated by Great Britain, France, Spain, Portugal, and the Dutch Republic. Slave-ships of the Atlantic slave trade transported captives for slavery from Africa to the Americas. Indigenous people were also enslaved in the North American colonies, but on a smaller scale, and Indian slavery largely ended in the late eighteenth century. Enslavement of Indigenous people did continue to occur in the Southern states until the Emancipation Proclamation issued by President Abraham Lincoln in 1863. Slavery was also used as a punishment for crimes committed by free people. In the colonies, slave status for Africans became hereditary with the adoption and application of civil law into colonial law, which defined the status of children born in the colonies as determined by the mother - known as partus sequitur ventrem. Children born to enslaved women were born enslaved, regardless of paternity. Children born to free women were free, regardless of ethnicity. By the time of the American Revolution, the European colonial powers had embedded chattel slavery for Africans and their descendants throughout the Americas, including the future United States. Native Americans Native Americans enslaved members of their own and other tribes, usually as a result of taking captives in raids and warfare, both before and after Europeans arrived. This practice continued into the 1800s. In some cases, especially for young women or children, Native American families adopted captives to replace members they had lost. Enslavement was not necessarily hereditary. Slaves included captives from wars and slave raids; captives bartered from other tribes, sometimes at great distances; children sold by their parents during famines; and men and women who staked themselves in gambling when they had nothing else, which put them into servitude in some cases for life. In three expeditions between 1514 and 1525, Spanish explorers visited the Carolinas and enslaved Native Americans, who they took to their base on Santo Domingo. The Spanish crown's charter for its 1526 colony in the Carolinas and Georgia was more restrictive. It required that Native Americans be treated well, paid, and converted