Question

when did Northern states ban slavery?

Answer 1

The first colony to ban slavery was Georgia, in 1735. The institution was reinstated in 1750.

The Vermont Republic banned slavery in 1777, while still a colonial proprietorship of Great Britain, although embroiled in the Colonial Civil War at the time.

Pennsylvania, in 1780, and Massachusetts in 1783 purported to abolish slavery within there jurisdictions. However, since both were British colonies at the time (and remained so until independence was granted by the British by means of the Treaty of Paris in 1783), the validity and legal efficacy of the abolition acts is questionable. After independence was granted, Connecticut and Rhode Island outlawed the practice, making them the first independent states to do so. However, the did so as independent nations of the confederacy created by the Articles of Confederation. The first state to enact abolition legislation after ratification of the US Constitution was New York, in 1799, although the legislation called for gradual emancipation and did not abolish slavery outright. In 1817, additional legislation was enacted that required the emancipation of all slaves in the state by 1827 (although sufficient loopholes existed to retain some in bondage if one analyzes the statute carefully).

The Compensated Emancipation Act was passed by Congress in April 1862 purported to abolish slavery in Washington DC. However, if tested in the Supreme Court, the Act should have been declared illegal and unconstitutional.

Although New Jersey "abolished" slavery in 1804, there were still slaves in bondage in the state when Amendment XIII was ratified. New Jersey was the last "northern" state to do so (unless one counts Maryland, Delaware, Missouri, Kentucky, Washington DC and, later, West Virginia among the ranks of the "north") As was the typical case, the New Jersey legislation called for gradual emancipation and abolition and even though the laws were on the books, slavery remained legal for decades after passage.

As a province of Mexico, Texas prohibited slavery. However, the Republic of Texas permitted the practice and slavery remained legal when the Republic attained statehood.

The right to own human chattel was guaranteed by the US Constitution (by Article I, Sections 2 and 9, Article IV, section 2, and Amendments IV, V, IX and X), which ought to prove the lie that the CSA states seceded in order to retain the slaves. IIf that isn't enough, in 1861, the Republican dominated northern majority in Congress passed the Corwin Amendment, which would have prohibited the introduction of any abolition amendment in the future. Rather than to stick around to ratify the amendment, the CSA states seceded.

The first attempt to amend the constitution to abolish slavery came in 1864, when the southern states were obviously absent. The measure failed. Even had it passed and been submitted for ratification, there was far less than sufficient support in the north for ratification.

Under the Full Faith and Credit Clause of the US Constitution, if a slave traveled to a free state with or without his/her master, the status as slave remained unchanged. Under Article IV, Section 2, if a slave made it to a free state, it was the absolute duty of anyone who came into possession of that slave to return it to the rightful owner, and it was the duty of the state to effectuate the by means of appropriate legislation and state agencies.

The Emancipation Proclamation was illegal and unconstitutional. It was also redundant, Congress having already purported to do the same thing (equally illegally and unconstitutionally) by the Confiscation Acts months earlier. Neither EP nor the Acts pretended to abolish slavery and, in fact, retained the institution intact in Tennessee, Missouri, Maryland, Delaware and Kentucky, as well as in large regions of Louisiana and Virginia. After announcement of EP, West Virginia was (illegally and unconstitutionally) admitted to the USA as a slave state. The EP and Acts were intended as weapons of war and had nothing whatsoever to do with human rights or morality.

Ratification of Amendment XIII, which, in December 1865, finally abolished slavery and emancipated all slaves, was coerced not as a human rights measure but as a tool of vengeance and was intended to so destroy the CSA states and to bankrupt the southern aristocracy such that the south could not soon rise again.

There's all kinds of neat stuff out there, if you're interested. It's all right there at you fingertips. On the other hand, if the question is for homework, I can't (won't) do it for you.