There is quite a bit of confusion about the dates in which slavery was abolished in the Northern states, because "abolishing slavery" meant different things in different states. (Theodore Weld, in his pamphlet opposing slavery in the District of Columbia, gives a detailed chronology.) It is true that beginning with the independent Republic of Vermont in 1777, all states north of the Ohio River and the Mason–Dixon line that separated Pennsylvania from Maryland passed laws that abolished slavery, although in some cases the process was scheduled to take decades to be fully effective. These included the first abolition laws in the entire New World: the Massachusetts Constitution, adopted in 1780, declared all men to have rights, making slavery unenforceable, and it disappeared through the individual actions of both masters and slaves. However what the abolition forces passed in 1799 in New York state was an Act for the "Gradual" Abolition of Slavery. New Jersey abolished slavery in 1804, but in 1860 a dozen blacks were still held as "perpetual apprentices". In the Northwest Ordinance of 1787, the Congress of the Confederation prohibited slavery in the territories northwest of the Ohio River. At the Constitutional Convention of 1787, slavery was the most contentious topic. Outright prohibition of slavery was impossible, as the Southern states (Georgia, South Carolina, North Carolina, Virginia, Maryland, and Delaware) would never have agreed. The only restriction on slavery that could be agreed on was the prohibition of the importation of slaves, and even that prohibition was postponed for 20 years. By that time, all the states except South Carolina had passed laws abolishing or severely limiting the importation of slaves. When 1808 approached, then-President Thomas Jefferson, in his 1806 annual message to Congress (State of the Union), proposed legislation, approved by Congress with little controversy in 1807, prohibiting the importation of slaves into the United States effective the first day the Constitution permitted, 1 January 1808. As he put it, this would "withdraw the citizens of the United States from all further participation in those violations of human rights...which the morality, the reputation, and the best of our country have long been eager to proscribe". However, about 1,000 slaves per year continued to be illegally brought (smuggled) into the United States; see Wanderer and Clotilda. This was primarily via Spanish Florida and the Gulf Coast; the United States acquired Florida from Spain in 1819, effective 1821, in part as a slave-control measure: no imports coming in, and certainly no fugitives escaping into a refuge.