Pennsylvania became the first official U.S. state to pass an emancipation law in 1780, with the passage of the Gradual Abolition Act. The law established that children subsequently born to slaves would be considered free, although it did not free enslaved African-Americans born before the law's existence. That model of "gradual emancipation" was eventually adopted by most Northern states, aside from Massachusetts, which instantly abolished the practice following a state Supreme Court decision in 1783. Under the Pennsylvania law, the children of slaves were considered “indentured servants” until the age of 28, when they were freed. Up until that point, they were still required to work for their mother’s slave owner.

Pennsylvania's Gradual Abolition Act

The Gradual Abolition Act aimed to phase out the practice of slavery in Pennsylvania while simultaneously respecting the so-called property rights of slave owners. The original 1780 act, in addition to changing the legal status of children born to slaves, prohibited the further importation of slaves into Pennsylvania. It also mandated the creation of a registry of all the slaves held in the state. Although slave owners were not required to free slaves they acquired before the passage of the law, they were forced to register their holdings on an annual basis to verify no additional human beings had been imported. The original law contained an exemption for members of the U.S. Congress and their personal slaves. Slavery did not become truly illegal in Pennsylvania until 1847, a point where almost 100 people in the state were still enslaved, according to the Independence Hall Association.

Northern States

Connecticut, New Hampshire, New York, New Jersey and Rhode Island all created legislation calling for the gradual abolition of slavery in the aftermath of Pennsylvania’s 1780 law. In 1783, all slaves in Massachusetts were instantly freed after the state's Supreme Court ruled the practice was made unconstitutional by the commonwealth's 1780 constitution. As a result, Maine – then a part of Massachusetts – was a free state upon entering the United States union in 1820. The Northwest Ordinance of 1787 prohibited slavery in the country's Northwest territory (what became Ohio, Indiana, Illinois, Michigan and Wisconsin).

The Case of Vermont

Although technically a colony at the time, Vermont was technically the first state – in this case, future state – to ban the importation and forced servitude of black slaves. The colony’s 1777 constitution prohibited slavery in its entirely, a response to the growing abolitionist movement in the North. However, according to the Smithsonian Museum, the language of the provision was vague enough to overlook the state’s already established slave trade in some circumstances. It also created complicated legal structures that enforced the discriminatory treatment of free blacks.

Federal Law

Neither the Articles of Confederation, which united the colonies in 1777 following their declaration of Independence, or the 1787 United States Constitution gave the national government the power to end slavery. Instead, it was outlawed on a state-by-state basis until President Abraham Lincoln’s 1863 Emancipation Proclamation, which banned slavery in the Confederate states challenging the Union during the Civil War. However, while the executive order is revered for supposedly ending slavery in the United States, the National Archives reports the law was extremely limited. The order only applied to states that had seceded from the Union (leaving some southern-border states untouched) and exempted parts of the Confederacy that had already come under Northern military control. The U.S. Constitution’s 13th Amendment, which legally abolished slavery and involuntary servitude across the nation, was ratified and adopted in 1865.