"We have not sought to extend our territorial possessions by conquest, or our republican institutions over a reluctant people. It was the deliberate homage of each people to the great principle of our federative union. If we consider the extent of territory involved in the annexation, its prospective influence on America, the means by which it has been accomplished, springing purely from the choice of the people themselves to share the blessings of our union, the history of the world may be challenged to furnish a parallel … We may rejoice that the tranquil and pervading influence of the American principle of self-government was sufficient to defeat the purposes of British and French interference … From this example European Governments may learn how vain diplomatic arts and intrigues must ever prove upon this continent against that system of self-government which seems natural to our soil, and which will ever resist foreign interference."—James Polk, from the State of the Union Address, December 2, 1845

One effect of the sense of American superiority described in this excerpt was

international backlash in the form of renewed hostilities on American soil
justification of the Mexican-American War
reluctance of the U.S. government to negotiate treaties with Canada
simplification of the immigration policies of the time