That's US' image worldwide too, or was. Except in the Muslim world where their atrocities were observed and reported firsthand. Wikileaks blew open that made-up image in a big way. Reminds me of:
"One of the artifices of devil is, to induce men to believe that he does not exist." -Charles Baudelaire.
The quote is best known in the modern day in the form it took in The Usual Suspects: "the greatest trick the devil ever pulled was convincing the world that he didn't exist".
Baudelaire did write the same thing, but it's not original to him either, making him an odd citation. In particular, the form you quote didn't come from Baudelaire; it came from John Wilkinson.
Wilkinson (1836): "One of the artifices of Satan is, to induce men to believe that he does not exist"
Baudelaire (1864): "la plus belle des ruses du Diable est de vous persuader qu’il n’existe pas!" ["the loveliest trick of the Devil is to persuade you that he doesn’t exist!"]
Also, the escalating violent struggle is making someone some serious money. So the monetary incentives are just as strong too whatever the overt justification may be.