At the time of the louisiana purchase, there was a dispute between president jefferson and france's napoleon. a balance in congress between free and slave states. a concern over doubling the size of the united states. a reluctance among people to move westward.

 A balance in Congress between free and slave states.

Explanation:

According to Dr. William Foley of Central Missouri State University, there had typically been a balance of representation between slave and free states. He says, "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."

So when the Louisiana Purchase was added to the land of the United States, that set in motion debates over whether states established in the newly acquired territories would be slave or free.  

The Louisiana Purchase territories were acquired from France in 1803.   Debates over the future of new states in that region continued for the next decade or more.  Missouri was a part of what was acquired in the Louisiana Purchase.  In 1820, when Missouri was ready to apply for statehood, a compromise was reached in Congress that established a plan for slave vs. free regions within the overall Louisiana Purchase regions.  The Missouri Compromise admitted Missouri into the Union as a slave state with Maine being added as a free state at the same time, to keep the balance of slave and free states equal.  It also prohibited any future slave states north of the latitude line 36 1/2 degrees north of the equator in territories of the Louisiana Purchase, with the exception of Missouri (north of that line) being admitted as a slave state.