Missouri Compromise was a plan agreed upon by the
United States Congress in 1820 to settle the debate over
slavery in the Louisiana Purchase area. The plan temporarily
maintained the balance between free and slave states.
In 1818, the Territory of Missouri, which was part of the
Louisiana Purchase, applied for admission to the Union.
Slavery was legal in the Territory of Missouri, and about
10,000 slaves lived there. Most people expected Missouri
to become a slave state. When the bill to admit Missouri to
the Union was introduced, there were an equal number of
free and slave states. Six of the original 13 states and five
new states permitted slavery, while seven of the original
states and four new states did not. This meant that the free
states and the slave states each had 22 senators in the
United States Senate. The admission of Missouri threatened
to destroy this balance.
This balance had been temporarily upset a number of times,
but it had always been easy to decide whether states east of
the Mississippi River should be slave or free. Mason and
Dixon's Line and the Ohio River formed a natural and
well-understood boundary between the two sections. No
such line had been drawn west of the Mississippi River. In
addition, some parts of Missouri Territory lay to the north
of the mouth of the Ohio River, while other parts of it lay to
A heated debate broke out in Congress when
Representative James Tallmadge of New York introduced
an amendment to the bill enabling Missouri to become a
state. Tallmadge proposed to prohibit the bringing of any
more slaves into Missouri, and to grant freedom to the
children of slaves born within the state after its admission.
This proposal disturbed Southerners, who found cotton
growing by means of slave labor increasingly profitable, and
feared national legislation against slavery. Because the free
states dominated the House of Representatives, the slave
states felt they must keep the even balance in the Senate.
The Tallmadge Amendment passed the House, but the
Senate defeated it. During the next session of Congress,
Maine applied for admission to the Union. Missouri and
Maine could then be accepted without upsetting the
Senate's balance between free and slave states, and the
Missouri Compromise became possible.
The compromise admitted Maine as a free state and
authorized Missouri to form a state constitution. A territory
had to have an established constitution before it could
become a state. The compromise also banned slavery from
the Louisiana Purchase north of the southern boundary of
Missouri, the line of 36 degrees 30 minutes north latitude,
except in the state of Missouri.
The people of Missouri believed they had the right to
decide about slavery in their state. They wrote a constitution
that allowed slavery and that restricted free blacks from
entering the state.
Before Congress would admit Missouri, a second Missouri
Compromise was necessary. Henry Clay, the Speaker of
the House, helped work out this agreement. It required the
Missouri legislature not to deny black citizens their
constitutional rights. With this understanding, Missouri was
admitted to the Union in 1821.
In 1848, Congress passed the Oregon Territory bill, which
prohibited slavery in the area. President James K. Polk
signed the bill because the Oregon Territory lay north of the
Missouri Compromise line. Later proposals tried to extend
the line by law across the continent to the Pacific Ocean.
These efforts failed. The Missouri Compromise was
repealed by the Kansas-Nebraska Act of 1854.