Was the Mexican War an Exercise in American Imperialism?

With this question, I was torn between both the "yes" and the "no" articles. Both of the articles had their strong points, but if I absolutely had to choose one, it would have to be the "yes" article. The yes article, written by Ramon Eduardo Ruiz, really gave more information on how the Mexican War was, in fact, an exercise of American imperialism. (Imperialism meaning the policy of extending the rule or authority of an empire or nation over foreign countries, or of acquiring and holding colonies and dependencies. {reference dictionary.com})
In the article, it mentioned how the United States' economic and strategic interests were at risk, along with democracy, if they didn't keep control of Oregon, Texas, and California. If they hadn't got those states, they wouldn't have been able to have more land for freedom and they would have to worry about another country having those states/territories and not being able to have the democracy that they wanted to have. Also, they wanted to keep the Europeans, mainly the British, from trying to stake their claim to the new territories, especially Oregon.
With Mexico, the Mexicans still believed that Texas was just a province in revolt and that it was still theirs. In order to make sure that Texas would be annexed, the United States did have to use their imperialism, and if it meant using warfare, so be it.
The Mexican War was an exercise of American Imperialism, not only because of wanting to acquire new states, but also because of expanding freedom and democracy.