Santo Domingo"), in which former slaves systematically murdered most of what was left of the country's white population—including men, women, children, and even many sympathetic to abolition—after the successful slave revolt in Haiti. Historian Thomas Fleming points to the historical phrase "a disease in the public mind" used by critics of this idea and proposes it contributed to the segregation in the Jim Crow era following emancipation. These fears were exacerbated by the 1859 attempt of John Brown to instigate an armed slave rebellion in the South. Abolitionists The abolitionists—those advocating the end of slavery—were active in the decades leading up to the Civil War. They traced their philosophical roots back to Puritans, who believed that slavery was morally wrong. One of the early Puritan writings on this subject was The Selling of Joseph, by Samuel Sewall in 1700. In it, Sewall condemned slavery and the slave trade and refuted many of the era's typical justifications for slavery. The American Revolution and the cause of liberty added tremendous impetus to the abolitionist cause. Slavery, which had been around for thousands of years, was considered normal and was not a significant issue of public debate prior to the Revolution. The Revolution changed that and made it into an issue that had to be addressed. As a result, during and shortly after the Revolution, the Northern states quickly started outlawing slavery. 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, which was the first day that the Constitution (Article I, section 9, clause 1) permitted Congress to prohibit the importation of slaves. Benjamin Franklin and James Madison each 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 and 1810 as a result of these actions. The establishment of the Northwest Territory as "free soil"—no slavery—by Manasseh Cutler and Rufus Putnam (who both came from Puritan New England) would also prove crucial. This territory (which became the