From the secondary source I found it says in order to have the same amount of slave and free states they made Missouri a slave state and made a new state called Maine a free state. Also with the exception of Missouri every state above the 36 30 line had to be a free state and everything below could be a slave state. By March 2 1820 all the bills were passed for this to happen. https://www.loc.gov/rr/program/bib/ourdocs/Missouri.html
In my Primary Source it says that the person who came up with the Missouri Compromise was Henry Clay. Henry Clay was the governor of Kentucky. He had made deals like this before so it wasn't weird that he came up with this one. http://www.historynet.com/missouri-compromise
This is the video I found
https://youtu.be/JTSbn5cE4LA
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