The
American Revolution and the cause of liberty added impetus to the abolitionist cause. Even in Southern states, laws were changed to limit slavery and facilitate
manumission. The amount of
indentured servitude dropped dramatically throughout the country. An
Act Prohibiting Importation of Slaves sailed through Congress with little opposition. President
Thomas Jefferson supported it, and it went into effect on January 1, 1808, the first day the Constitution permitted Congress to prohibit importation of slaves.
Benjamin Franklin and
James Madison helped found manumission societies. Influenced by the Revolution, many slave owners freed their slaves, but some, such as
George Washington, did so only in their wills. The number of free black people as a proportion of the black population in the
upper South increased from less than 1 percent to nearly 10 percent between 1790-1810.