Prohibited slavery north of a specific boundary established by the government

the Mason-Dixon line

Explanation:

In the past, United States were divided into 2 regions:

- Slave states.

The states where slavery was considered to be legal. (mostly located on Southern part of United States)

- Free States

The states where slavery was considered to be illegal (mostly located on Northern Part of United States)

The Mason-Dixon line was the name of the boundaries that separated these two regions. The line spread across the northern border of Missouri, Kentucky, and West Virginia. Every states above this line was considered to be free states while the states below the line was considered as Slave states.