In the District of Columbia, the slave trade was legal from its creation until it was outlawed as part of the Compromise of 1850. That restrictions on slavery in the District were probably coming was a major factor in the retrocession of the Virginia part of the District back to Virginia in 1847. Thus the large slave-trading businesses in Alexandria, such as Franklin & Armfield, could continue their operations in Virginia, where slavery was more secure.
Ownership of enslaved people remained legal in the District. It was not until the departure of the legislators from the seceding states that Congress could pass in 1862 the District of Columbia Compensated Emancipation Act. The Act provided partial compensation, up to $300 per slave, to slave owners.[1] It was paid from general federal funds. Even though the compensation was small, as before the war a productive slave was worth much more than $300,[2][3] it is the only place in the United States where slave owners received any compensation at all for freeing their slaves. Some slave owners, rather than manumitting (freeing) their enslaved workers for this small compensation, took them to Virginia and more profitably sold them there, which was completely legal.
Abolitionists, led by Massachusetts Representative and former President John Quincy Adams, focused on eliminating slavery in the District. They argued that the Constitution gave Congress full control over the laws of the District, including laws regarding slavery. States' rights was not a factor because the District was not a state. As Southern legislators realized, it was the first step toward outlawing slavery everywhere. The Emancipation Proclamation came five months after slavery ended in the District.
The drive to eliminate slavery in the District of Columbia was a major component in the anti-slavery campaign that led to the Civil War. Congress, under the leadership of former president John Quincy Adams, now Representative from strongly anti-slavery Massachusetts, was flooded with many petitions for action on the subject. They passed the gag rules, automatically tabling the petitions and preventing them from being read, discussed, or printed. Rather than resolving anything, these rules outraged Northerners and contributed to the growing polarization of the country over slavery.