The Missouri Crisis began when the Missouri Territory applied for statehood in 1818. Missouri bid to become the first state west of the Mississippi River, as well as a slave-state.
Both Southern slaveholders and Northern opponents of the spread of slavery were concerned about this addition. Northerners were interested in stopping the spread of slavery, which meant that they did not want the new state to allow it. Moreover, they believed that this would upset the balance of power in Congress. On the other hand, Southerners argued that new states should be given the freedom to choose slavery within their territory or not. The conflict triggered threats of disunion and war, until the crisis was diffused through the adoption of the Missouri Compromise.