The three correct statements are:
B. One argument against American imperialism was that it would be costly to maintain territory outside American borders.
C. Social Darwinism was the concept that the United States and Western powers were better suited to govern other parts of the world and would bring civilization.
E. Increasing trade and opening up new markets was a major argument in favor of American imperialism.
The other statements are incorrect: A is incorrect because Theodore Roosevelt was not a founder of the Anti-Imperialist League; D is incorrect because Hawaii was not purchased from Russia but rather was annexed by the United States after a coup by American settlers.