I've been writing an essay for school and I've been wondering what did sectionalism have to do with the American Civil War? Does sectionalism include the Missouri Compromise and the breaking away of the South? If not, what are some other examples?
Sectionalism was in fact a major element of the civil war. At the risk of oversimplifying, the strongest conflict was between the Northeastern industrial states (New England, New York, Pennsylvania, and New Jersey), and the "South,"( basically the 11 states that made up the Confederacy). In addition, there were two other sections: the Midwest, and border states such as Maryland, Delaware, Kentucky, and Missouri.
President Thomas Jefferson (a Virginian), feared that the Midwestern states (and "Middle South: states such as Tennessee and Mississippi), might try to break away from the 13 colonies and form a connection, either among themselves, along the Ohio and Mississippi rivers, or with British Canada over the Great Lakes, and down the St. Lawrence River. That's why he was so eager to purchase New Orleans to mollify them. (He actually made the "Louisiana" purchase.)
Other Southerners initially felt that the "agricultural" (food-producing) Midwest would find common cause with the "agricultural" (cash crop) South against Northeastern industrial and banking interests. In this regard, the Mississippi River might unite the Midwest and South, against the Northeast.
But the building of the Erie canal connecting the Great Lakes and the Hudson River pushed the Midwest agricultural trade to the Northeast. The Midwesterners found that Northeasterners needed more (and paid better for) their wheat than the South, which preferred its own corn. Also, Northeastern woolens suited the cold climate Midwest better than Southern cotton (in the days before central heating).
And Midwesterners felt that southern slave (and cash crop) agriculture undercut their (food) farming practices, and therefore considered the South competitive with, rather than complementary to themselves. Hence, the Midwest ultimately sided with the Northeast in the Civil War.
The rift between slave and free agriculture was particularly acute in the border states, e.g. in Missouri, and in Maryland between the pro-union Piedmont and the pro-slavery Tidewater regions. Most of the above mentioned border states had mini "civil wars" that were resolved in favor of the North. West Virginia "seceded from secession" (Confederate Virginia) and joined the North.
In the end, three regions, the Northeast, Midwest, and border states, plus the isolated western states of California and Oregon joined together and "ganged up" against the 11 Confederate states, thereby giving the civil war its character.