<P> Slavery was a common practice in the Americas prior to the arrival of Europeans, as different American Indian groups captured and held other tribes' members as slaves . Many of these captives were forced to undergo human sacrifice in Amerindian civilizations such as the Aztecs . In response to some enslavement of natives in the Caribbean during the early years, the Spanish Crown passed a series of laws prohibiting slavery as early as 1512 . A new stricter set of laws was passed in 1542, called the New Laws of the Indies for the Good Treatment and Preservation of Indians, or simply New Laws . These were created to prevent the exploitation of the indigenous peoples by the encomenderos or landowners, by strictly limiting their power and dominion . This helped curb Indian slavery considerably, though not completely . Later, with the arrival of other European colonial powers in the New World, the enslavement of native populations increased, as these empires lacked legislation against slavery until decades later . The population of indigenous peoples declined (mostly from European diseases, but also from forced exploitation and atrocities). Later, native workers were replaced by Africans imported through a large commercial slave trade . </P> <P> By the 18th century, the overwhelming number of black slaves was such that Amerindian slavery was less commonly used . Africans, who were taken aboard slave ships to the Americas, were primarily obtained from their African homelands by coastal tribes who captured and sold them . Europeans traded for slaves with the slave capturers of the local native African tribes in exchange for rum, guns, gunpowder, and other manufactures . </P> <P> The total slave trade to islands in the Caribbean, Brazil, Mexico and to the United States is estimated to have involved 12 million Africans . The vast majority of these slaves went to sugar colonies in the Caribbean and to Brazil, where life expectancy was short and the numbers had to be continually replenished . At most about 600,000 African slaves were imported into the U.S., or 5% of the 12 million slaves brought across from Africa . Life expectancy was much higher in the U.S. (because of better food, less disease, lighter work loads, and better medical care) so the numbers grew rapidly by excesses of births over deaths, reaching 4 million by the 1860 Census . Slaves were a valuable commodity both for work and for sale in slave markets and so the policy of actively encouraging or forcing slaves to breed developed, especially after the ending of the Atlantic slave trade . From 1770 until 1860, the rate of growth of North American slaves was much greater than for the population of any nation in Europe, and was nearly twice as rapid as that of England . </P> <P> Slaves imported to the Thirteen colonies / United States by time period: </P>

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