Slavery began in the United States during the colonial era, in the early 1600s. European colonists brought enslaved Africans to the Americas, primarily to work on tobacco and cotton plantations. Slavery was legal in all of the American colonies, and later in several states after the United States gained independence in 1776. It gradually spread westward as new territories were acquired by the U.S. government. The institution of slavery persisted in the country until the abolition of slavery was achieved through the passage of the 13th Amendment to the U.S. Constitution in 1865.