"since . . cultural and political movements failed to achieve a binding national unity, a militant campaign of whiteness rapidly emerged as [andrew] jackson’s principal safeguard of white american identity. . in the national culture . . racial mixture rapidly moved to a central focus of public concern because it was the only thing the great majority of white americans genuinely agreed on—that mixture was wrong. racial unity had always been important, but now racial purity became the elixir of national salvation. national consciousness was now shaped not just by fearfulness about the ‘blackness’ of indians, but especially about the mixed bloods. they were not only ‘black,’ they were ‘black hearted’ in their . . attitudes towards whites, and they threatened to pollute whites’ bloodstream by intermixture." — thomas ingersoll, historian, to intermix with our white brothers: indian mixed bloods in the united states from earliest times to the indian removals, 2005 the point of view illustrated by the excerpt was most likely a reaction to which of the following developments occurring in the united states at that time?