Final answer:
Sectionalism in the early 19th century United States was marked by regional loyalty and conflict over issues such as economic interests and slavery, leading to increasing tensions and ultimately the Civil War.
Step-by-step explanation:
Sectionalism is a term that refers to the loyalty to a particular region or section of a country, rather than to the country as a whole. In the context of the United States during the 1820s, sectionalism grew as a result of conflicting economic interests, cultural values, and the contentious issue of slavery. This divide was predominantly between the Northern states, which were industrializing and had largely abolished slavery, and the Southern states, which were dependent on slave labor for their agricultural economy.
During this period, debates over the expansion of slavery into new territories and states led to increased tensions. The Missouri Compromise in 1821 and the Compromise of 1850 were temporary measures to maintain a balance between free and slave states, but they did not address the underlying issues. Political differences, economic interests, and moral perspectives on slavery deepened the sectional divide, leading to further conflicts and ultimately contributing to the outbreak of the American Civil War in the 1860s.
Final answer in two line explanation in 300 words: Sectionalism in the early 19th century U.S. refers to the division and loyalty to one's region (North or South), primarily over issues like economic interests and slavery, which paved the way to the Civil War.