There are two kinds of Riya - Showing off-Ostentation ie pure ostentation and adulterated ostention. In pure ostentation "Riya" a man does a good deed only for worldly benefit. In Adulterated ostentation, a man does a good deed with the intention of reaping the benefits of the world as well as of the Hereafter.
My speculation is that the U. S. does not want to establish the principle that it has to defer to some higher authority before carrying out the use of violence.