The legal institution of human chattel slavery, comprising the enslavement primarily of Africans and African Americans, was prevalent in the United States of America from its founding in 1776 until 1865, predominantly in the South. Slavery was established throughout European colonization in the Americas. From 1526, during early colonial days, it was practiced in what became Britain's colonies, including the Thirteen Colonies that formed the United States. Under the law, an enslaved person was treated as property that could be bought, sold, or given away. Slavery lasted in about half of U.S. states until abolition. In the decades after the end of Reconstruction, many of slavery's economic and social functions were continued through segregation, sharecropping, and convict leasing. By the time of the American Revolutionary War (1775–1783), the status of enslaved people had been institutionalized as a racial caste associated with African ancestry. 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 and the Electoral College votes of slaveholding states. The Fugitive Slave Clause of the Constitution—Article IV, Section 2, Clause 3—provided that, if a slave escaped to another state, the other state had to return the slave to his or her master. This clause was implemented by the Fugitive Slave Act of 1793, passed by Congress. All Northern states had abolished slavery in some way by 1805; sometimes, abolition was a gradual process, a few hundred people were 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. It has been estimated that about 30% of congressmen who were born before 1840 were, at some time in their lives, owners of slaves. The rapid expansion of the cotton industry in the Deep South after the invention of the cotton gin greatly increased demand for slave labor, and the Southern states continued as