How do you think violence has been justified in The United States and which discourses have tried to justify violence in American history?
In addition to the ideas of the first poster, I would like to add the recurring 20th-century phrase "fighting for freedom." This phrase has an amazing currency, reappearing in the phrases below, among many others:
"making the world safe for democracy"
"arsenal of democracy"
"liberation of Iraq"
"fight for democracy"
I'm not trying to be critical of any one or more specific military campaigns of the United States, but I do think it's interesting how the focus in the modern era seems to be again and again on freedom.
The "taming" and "settling" of the frontier is a second, earlier discourse, one that dominated many nineteenth-century discussions of North America.
The link provided below offers a discussion of this topic is some detail.
Violence has typically been justified in the United States in a number of ways. Most prominently, (in international affairs) it has been justified by the idea that the United States is special and is superior to other countries -- particularly those that are not Western European in culture.
You can see this is the idea of Manifest Destiny. This idea held that it was the destiny of the United States to rule the continent because its culture and values were superior to those of the Indians and the Mexicans. This was used to justify the Mexican-American War and the wars against the Indians.
As far was which discourses, I think you would have to specify some options because I, at least, do not know what kinds of discourses you are referring to here.