What did the Missouri Compromise propose?

It was a negation between the north and south as to what states could be slave states and which ones couldn't

The Missouri Compromise of 1820 was both a negotiated political and legal solution. The US was already divided over the issue of slavery. Congress admitted Missouri to be part of the US as a state with legal slavery. At the same time, it admitted Maine as a free state. It was a very delicate act of balance. The congressional law also banned slavery in the remaining territories of the Louisiana Purchase north of the 36º 30' parallel.