In foreign policy, perhaps the best example of nationalism during this time was the Monroe Doctrine. This statement of US policy, announced in 1823, showed the US trying to assert itself as an important nation that could tell other countries, including powerful countries of Europe, what to do. It is typically seen as a statement of American nationalism and ambition.
At home, a major example of nationalism was the rejection of the Federalist Party after the War of 1812. This party came to be seen as one that catered exclusively to the sectional interests of New England. As Americans came more and more to feel that all the states were united as one country, they rejected this sectionalism (though it was, of course, to arise again in the prelude to the Civil War).