What was the most controversial aspect of the American System in the early 19th century?

The most controversial aspect of the American System in the early 19th century was its emphasis on federal funding for internal improvements, such as roads and canals. Critics argued that this centralization of power encroached on states' rights and questioned the constitutionality of using federal funds for state projects. Additionally, the protective tariffs intended to foster American industry were contentious, as they benefited some regions while harming others, particularly in the agrarian South. This division contributed to growing sectional tensions leading up to the Civil War.