In 1803, Thomas Jefferson purchased 828,000 acres of land for over 11 million dollars known as the Louisiana Purchase. The Purchase of the lands helped the nation socially and economically, but it also brought new challenges for people within the states and even within the government.
Each state that is annexed in the United States has to settle wether it is a free or slave state. Before the Missouri Compromise the slave states and free states equalled eachother, therefore they had equal representation in the senete and so one party does not overpower another.
This allows for every party in the government and even common people to have closure so that a civil dispute does not break out. After the purchase of land Louisiana was accepted as a slave state this equalled the balence until Missouri wanted to enter state hood and declare itself a slave state. This would mean unequal representation which both parties knew it was a key factor in keeping the issue of slaves in order.
This issue remained until Main wanted to declare statehood as a free state, but many argued if Maine is wants to be a free state then Missouri should be a slave state. This was officially known as the Missouri Compromise, Maine is a free state and Missouri is a slave state.
With this no slavery in the other states outside the Louisiana purchase can be allowed. Even though this was a short solution to a big problem it calmed people down about the split between free and not free states.
It was a way for the senate to diffuse the situation of slavery for little time and it also set a new stage in Senate history. Before the Missouri compromise the House of Representatives would overstep the Senate and cast a shadow over them.
Later on Henry Clay who served in the senate moved to the House of Representatives and was elected speaker of the house. Henry Clay oversaw the Missouri Compromise first hand when it was first introduced to him.
The House appealed for Missouri to come in as a no slavery state while the Senate wanted missouri to be a slave state, therefor both sides were at a stalemate. Since there was a stalemate the issue died at first but then reopened in 1820 where Henry Clay was the one to create the compromise that Maine should be a free state and Missouri will be allowed to have slavery.
Pro slavery advocates wanted to change the compromise to benefit themselves but Clay sneakily signed the compromise and sent it to the Senate to be approved. Henry Clay founded the new era of the Senate because he sparked up new debates and helped create pro Union compromises.
https://www.senate.gov/artandhistory/history/minute/Missouri_Compromise.htm