The Texas war for independence, Mexican American War, Boxer Rebellion, Spanish American War, any number of little actions in Latin America form the late 1800's through Panama, Chile, Nicaragua, Haiti, and likely a few other places. I'm quite sure that most Native Americans didn't think of themselves as the aggressor through most of the 19th Century.
Well, as a case by case basis:
Texas War of Independance? huh? US wasn't involved there at all? Texas declared independance, we recognized it.
Mexican-American War was just an extension of the Texas war of independance. US annexed Texas (granted, an aggressive act), but Texas approved the annexation. Mexico didn't, and invaded.
Boxer rebellion. Huh? What the hell are you talking about? A certain cultlike group of native chinese decide to try and execute everyone in the country not pure-blood chinese (including US diplomats). Sounds like defensive action to me!
Spanish-American War. Sorry, but remember the Maine? Everybody then sure did!
As far as the Native Americans go, the only argument I could make there was that there was no single, recognized, sovereign nation that was being violated in an act of American agression like the current situation. Not that it makes what happened excusable (indeed, I maintain to this day the world would be a better place if the colonists had stopped at the Appalachians), but it IS a different situation.