by Drew VandeCreek, Ph.D.

In the Mexican-American War the United States decisively defeated the Republic of Mexico and acquired over five hundred thousand square miles of new territory that today comprises much of the nation's Southwest. The conflict emerged from many Americans' belief that their "Manifest Destiny" pointed toward a nation of continental scope, stretching from Atlantic to Pacific. While the seizure of new territories provided Americans with new lands for settlement, this development also exacerbated the growing sectional conflict over the expansion of slavery. Northerners and southerners grappled in Congress and at the polls in hopes of shaping the new territories in the image of their own social order. Unable to resolve the matter of the Mexican Cession's future by political means, the two sections took up arms in 1861 in the American Civil War.