Why did the Northwest Ordinance of 1787 (Article 6) prohibit slavery in the Northwest Territory?

Question

Slavery was legal in most of the states at the time. What was the reasoning that prohibited the institution in the country’s only territories?

http://www.earlyamerica.com/earlyamerica/milestones/ordinance/text.html

Answer 1

1) by 1787 the Northern states had acted to at least move toward abolishing slavery, and did not wish to see it spread. So there was solid Northern support for NEW states to begin without slavery.

http://www.slavenorth.com/emancipation.htm
see the left sidebar links for info on emancipation in the inidividual states

2) At the time of the Revolution -- and even more so because of Revolution ideasls -- the idea that slavery was an evil, even if a necessary one, and the desire to see it end/die out was shared by many in the South This included a number of leaders, e.g., Washington and Jefferson. (The strong PRO-slavery view -- that the South's "peculiar institution" was a GOOD thing-- developed much later, with folks like John Calhoun in the 1830s.)

3) The country actually owned a comparable bit of land BELOW the Ohio River, which was expected to soon become slave states (beginning with Kentucky and Tenessee). In a sense, the 'balancing' of slave and free states associated with, the Missouri Compromise,,etc, was already beginning

map:
http://en.wikipedia.org/wiki/Image:Poster_united_states_1783_1803_shephard1923.png

'pairs of slave & free states'
http://en.wikipedia.org/wiki/Slave_states#Slave_and_free_state_pairs

Note that, just as most settlers South of the Ohio were from the Southern states, so the settlers in the Northwest Territory were chiefly from the Northern states.

4) at about the time the Ordinance passed (July 1787) delegates to the Constitutional Convention were meeting, and ironing out issues of North vs. South. In particular, it has been suggested that the passage of the Northwest Ordinance was something of a payback for Northern agreement to the 3/5 Compromise (a provision that increased Southern representation in Congress, and hence its power in the national government.

In fact, at this time the South expected to keep pace with the North in growth, and with the added strength in Congress (and wiith that additional electors for choosing the President) the South had considerable political clout and expected to keep it. (As it turned out, immigration to the North far outripped that to the South, but no one had anticipated that.)

Answer 2

It was largely based on a plan proposed by Thomas Jefferson although the anti-slavery provision he advocated was defeated buy a vote of seven states to six.
Colonial history tells that the abolition battle preceded the Declaration of Independence. The New England states were vehement in opposition to slavery while it was still practiced in places like New York City and Philadelphia.
It may have also addressed a practice that was not uncommon among some of the native tribes.

Answer 3

I found this on wiki... its not much, but it might help support the article you linked too.

"In the decades preceding the American Civil War, the abolition of slavery in the northeast by the 1830s created a contiguous region of free states to balance the Congressional power of the slave states in the south. After the Louisiana Purchase, the Missouri Compromise effectively extended the Ohio River boundary between free and slave territory westward from the Mississippi to the Rocky Mountains. The balance between free and slave territory established in the ordinance eventually collapsed following the Mexican-American War."

Dan

P.S. There is also a link to another site as well as link to a recreation of the original doc at the bottom of the wiki page

http://www.econlib.org/library/ypdbooks/lalor/llCy787.html