slavery in the united states was the legal institution of human slavery in the united states. slaves were mostly africans and african americans. slavery existed in the united states of america in the 18th and 19th centuries. slavery existed in british america from early colonial days. slavery was legal in all thirteen colonies at the time of the declaration of independence in 1776. it lasted in about half the states until 1865. this was when it was banned in the entire country by the thirteenth amendment.