Slavery divided the United States along sectional lines between 1820 and 1860 because it created a critical rift between Northern and Southern states. Those in the North generally wanted slavery to end, or at least not expand into new territories. Those in the South wanted slavery to continue and be...
able to expand into new states.
In 1820, with the Missouri Compromise, the federal government tried to defuse the sectional divide over slavery. This law attempted to balance Northern and Southern interests by making Maine a free state, Missouri a slave state, and forbidding slavery in the rest of the Louisiana Purchase lands (territory that the government bought from France in 1803) north of the 36º 30’ parallel.
Three decades later, the United States had to decide what to do with the land that it seized in the Mexican-American War. As in 1820, the federal government tried to compromise. California was admitted into the Union as a free state. The citizens of Utah and New Mexico could vote on whether slavery would be allowed in their states.
To further placate the South, the federal government passed the Fugitive Slave Act of 1850. This law compelled federal officials to aid in the capture of slaves, or alleged slaves, who escaped North. The bill exacerbated the sectional divide since it increased hostilities between the North, the South, and the federal government.
American historian James M. McPherson tells the story of a teen slave named Thomas Sims. In February 1851, Sims ran away from his owner in Georgia and got a job as a waiter in Boston. Months later, Sims’s owner located him. Due to the Fugitive Slave Act, he was able to bring Sims back to the South with the assistance of hundreds of armed deputies and soldiers.
The force with which the Fugitive Slave Act was executed did not help matters. The act and the previous compromises didn't effectively tame the tension between the clashing sections. In 1858, Abraham Lincoln declared, "A house divided against itself cannot stand." In 1860, Lincoln was elected president and Southern states started succeeding from the Union. After decades of trying to resolve the sectional divide with painstaking compromises and acts, the United States would now try to resolve the sectional divide through war.