The Myth of Colonial Intents

"It's important to remember that the United States is the only country in the world that was founded was an empire. George Washington described it as a rising empire and because of that they had to conquer the national territory - this is imperialism - they didn't have to cross the oceans, but besides that, it's the standard imperialism. They practically exterminated the population that lived in these territories and stole half of Mexico's land"
- Noam Chomsky here  (I'm translating back to English from Portuguese from Spanish...)

I often hear that the United States were a country with origins in which its colonial inhabitants worked towards cultivation, whereas Brazil was an aftermath of colonial exploitation. Could that be a myth that we accepted too promptly? I believe so, and I have to stop and rethink History as I learned.
  The consequence of the United States being a country with the seeds of cultivation would be that there was a project of country in which "the other" was seen as a partner in the nation building process. Well, I think that the treatment of Native Americans, Mexicans and Africans proves that wrong.