Was the Mexican War an Exercise in American Imperialism?

I have to agree with Ramon Eduardo Ruiz. He says that when conquering Mexico's northern territories, the US waged an aggressive war against Mexico and Mexico never recovered from it. To him, Manifest Destiny showed the racism towards African and Mexican Americans who stood in the way of the White's land. Other factors made Americans think expansion. They were led to believe that the Union gained in stability as the number of states multiplies so they wanted to gain Texas and fight the Mexicans for their land. Ruiz also makes the beset argument because he points out flaws that Graebner had and how it wasn't all Polk's fault that we went to war for more land and states.