Slavery in the United States was the legal institution of human chattel slavery, comprising the enslavement primarily of Africans and African Americans, that existed in the United States of America from its founding in 1776 until the passage of the Thirteenth Amendment in 1865. Slavery was established throughout European colonization in the Americas. From 1526, during early colonial days, it was practiced in Britain’s colonies, including the Thirteen Colonies which formed the United States. Under the law, an enslaved person was treated as property and could be bought, sold, or given away. Slavery lasted in about half of U.S. states until 1865. As an economic system, slavery was largely replaced by sharecropping and convict leasing.
 During and immediately following the Revolution, abolitionist laws were passed in most Northern states and a movement developed to abolish slavery. The role of slavery under the United States Constitution (1789) was the most contentious issue during its drafting. Although the creators of the Constitution never used the word “slavery”, the final document, through the three-fifths clause, gave slave-owners disproportionate political power by augmenting the congressional representation of slaveholding states.
 All Northern states had abolished slavery in some way by 1805; sometimes, abolition was a gradual process, and hundreds of people were still enslaved in the Northern states as late as the 1840 Census. Some slaveowners, primarily in the Upper South, freed their slaves, and philanthropists and charitable groups bought and freed others. The Atlantic slave trade was outlawed by individual states beginning during the American Revolution. The import-trade was banned by Congress in 1808, although smuggling was common thereafter.[3
]: 7 It has been estimated that about 30% of congressmen who were born before 1840 were, at some time in their lives, owners of slaves. This is argued to have affected the progress of legislation against slavery.