Why did some believe that U. S expansion was needed to preserve the "American sprit" ?

Why did some believe that US expansion was needed to preserve the "American Spirit?" They thought that America would need a strong navy to protect the markets. Also, in Alfred Mahan's book, The Influence of Sea Power Upon History, he says that America's future would rely on gaining new markets abroad.

Explanation:

lincoln presided over the union victory in the american civil war, which dominated his presidency. a former whig, lincoln ran on a political platform opposed to the expansion of slavery in the territories. his election served as the immediate impetus for the outbreak of the american civil war.

the fourteeth amendment does not extend all bill of rights protection to the us -apex ur welcome