why was so important the division line in the united states in the mid-1800?

Answer 1

The dividing line between MD and PA was established in the late 1700's and was called The Mason-Dixon line. It later became symbolic of the division between the "free states" and "slave states" from the Missouri Compromise until the end of the American Civil War.

Answer 2

y a treaty signed on Apr. 30, 1803, the United States purchased from France the Louisiana Territory, more than 2 million sq km (800,000 sq mi) of land extending from the Mississippi River to the Rocky Mountains. The price was 60 million francs, about $15 million; $11,250,000 was to be paid directly, with the balance to be covered by the assumption by the United States of French debts to American citizens.