Final answer:
Option (a), Sectionalism refers to the division of the United States along geographic and economic lines, particularly over the issue of slavery. This growing rift led to tensions that compromises could no longer alleviate, eventually resulting in the Civil War.
Step-by-step explanation:
Sectionalism in Antebellum America
Sectionalism during the antebellum period in America refers to the growing division and tensions between different regions, primarily between the Northern and Southern states. These divisions were largely based on geographic, economic, and social differences, most notably on the issue of slavery. In antebellum America, sectionalism manifested in fierce debates over the expansion of slavery into new territories, differing economic interests, the balance of power between state and federal governments, and moral questions about the institution of slavery itself.
During the period from 1815 to 1840, American leaders attempted to minimize these divisions with various compromises, such as the Missouri Compromise and later the Compromise of 1850. However, these were temporary solutions that did not address the underlying issues. The sectional crisis eventually escalated to a point where compromise was no longer viable, leading to the disunion and the onset of the American Civil War in the 1860s. Key events, such as the Dred Scott decision and John Brown's raid, along with the emergence of the Republican Party and the election of Abraham Lincoln, accelerated the collapse of the sectional balance.