How did European Imperialism affect American Politics?
Some might argue that every aspect of American Imperialism is an offshoot of European Imperialism. If one is to compare the idea of American "exceptionalism" to the ideas that politicians and other leaders used to justify European expansion into the Americans and Africa and elsewhere, the arguments are not too dissimilar.
It was under the guise of a paternalistic idea that much of European colonialism justified its economic and political expansion into various other continents, and the same idea was used to justify American expansion though it may have been slightly modified with the idea that somehow the United States constitution or other founding principles gave it the right to influence politics or take territories abroad.
One might also argue that American Imperialism benefitted from the mistakes of European Imperialism in that the United States never tried to take over and manage a colony as large as India. Yet the United States still intervened in Vietnam despite watching the French failure there and one might argue that the U.S. ignored centuries of Imperialist failures by getting involved in Afghanistan.