By definition, sectionalism is the idea that one is loyal to a state, region, community, etc than the entire country as a whole. The idea of sectionalism was a huge problem during the Antebellum, Civil War, and Reconstruction eras in American history. In short, "section" relates to "sectionalism" because people are choosing to associate themselves with a particular group (ex. a Texan may say they are from the South than from the United States) rather than an entire system as a whole. Hope this helps you!