book The Struggle For Equality, historian James M. McPherson defines an abolitionist "as one who before the Civil War had agitated for the immediate, unconditional, and total abolition of slavery in the United States". He does not include antislavery activists such as Abraham Lincoln or the Republican Party, which called for the gradual ending of slavery. Benjamin Franklin, a slaveholder for much of his life, became a leading member of the Pennsylvania Society for the Abolition of Slavery, the first recognized organization for abolitionists in the United States. Following the American Revolutionary War, Northern states abolished slavery, beginning with the 1777 Constitution of Vermont, followed by Pennsylvania's gradual emancipation act in 1780. Other states with more of an economic interest in slaves, such as New York and New Jersey, also passed gradual emancipation laws, and by 1804, all the Northern states had abolished it, although this did not mean that already enslaved people were freed. Some had to work without wages as "indentured servants" for two more decades, although they could no longer be sold. Also in the post-Revolutionary years, individual slaveholders, especially in the Upper South, manumitted slaves, sometimes in their wills. (In the Deep South manumission was made difficult; in South Carolina every manumission required legislative approval, and the freed slaves had to leave the state immediately.) Many noted that they had been moved by the revolutionary ideals of the equality of men. The number of free black people as a proportion of the black population increased from less than one percent to nearly ten percent from 1790 to 1810 in the Upper South as a result of these actions. The 1836–1837 campaign to end free speech in Alton, Illinois culminated in the 7 November 1837 mob murder of abolitionist newspaper editor Elijah Parish Lovejoy, which was covered in newspapers nationwide, causing a rise in membership in abolitionist societies. By 1840 more than 15,000 people were members of abolitionist societies in the United States. In the 1850s in the fifteen states constituting the American South, slavery was legally established. While it was fading away in the cities as well as in the border states, it remained strong in plantation areas that grew cotton for export, or sugar, tobacco, or hemp. According to the 1860 United States Census, the slave population in the United States had grown to four million. American abolitionism was based in the North, although there