But stopping there is to make things too clear-cut. After all, the only reason the Mexican government “had” that territory in the first place was because a violent Spanish Empire had conquered or claimed it previously—and the government in Mexico City “inherited” it. Mexico was many nations and peoples smashed unnaturally into one “nation” by a coercive central authority (one that was constantly quelling internal rebellions!), and the vast majority of territory later taken by the U.S. was not inhabited by actual Mexicans (but rather by American Indians!). So how exactly was the Mexican claim any less imperialist than the U.S. one?

With patience, the combination of migration and territorial purchases could have seen the U.S. acquire much—even all—of this territory without a war. Instead, the U.S. embarked upon its first true war of conquest even as the seeds of civil war were sown.

History is muddy!