By this act Mason and Dixon's Line was extended through the Louisiana Purchase.

As the western boundary was then defined, slavery could still be extended into Arkansas and into a part of what is now Oklahoma, while a great empire to the northwest was reserved for the formation of free States.

Arkansas became a slave State in 1836 and Michigan was admitted as a free State in the following year.
With the admission of Arkansas and Michigan, thirteen slave States were balanced by a like number of free States.

The South still had Florida, which would in time become a slave State.

Against this single Territory there was an immense region to the northwest, equal in area to all the slave States combined, which, according to the Ordinance of 1787 and the Missouri Compromise, had been consecrated to freedom.