Final answer:
Transportation improvements in the early 19th century, including canals and railroads, favored the North and West, leading to sectionalism by marginalizing the Southern economy and exacerbating economic and political tensions.
Step-by-step explanation:
In the early 1800s, transportation improvements such as canals and railroads contributed to sectionalism in the United States by favoring the connections between the North and West, at the expense of the South. This enhanced the North's industrial economy and connected Western agricultural regions to Eastern markets, while the South's plantation economy felt increasingly marginalized. Projects like the Erie Canal and the expanding railroad infrastructure shifted economic power and growth towards the Northern and Western states. As a result, the South, which remained agrarian and relied on slave labor, began to feel economically and politically isolated, contributing to rising sectional tensions that would eventually lead to the Civil War.