Beat! Beat! Drums!... Wait... no... don't do that!

I think it is interesting to see how Whitman has written this entire poem in imperative form. He, in a literal sense, is telling the drums to keep beating and the bugles to keep on blowing. He is commanding the troops to continue ravaging the cities and to make unhappy the lives of those living there. "Mind not the timid--mind not the weeper or prayer." He, by using this form of speech, is almost personifying himself as the General of all things raucous and belligerent. Whitman is placing himself into the persona of that which he despises, and magnifying the militant, mercenary ambitions that he believes to exist there.
He moves his readers by commanding his supposed infantry to destroy and to disregard all things common folk hold dear. He tells them to, "leave not the bridegroom quiet--no happiness must he have now with his bride." Whitman knows where his readers invest their emotions, and he exploits that compassion and charity by transforming it into contempt for those that threaten this lock box of love. He seems to be, however, very careful as to how far he is willing to take this role-play. He never completely oversteps his bounds and is very tactful in drawing the line to demarcate how far is too far.
Whitman was a man very in touch with the his own sentiments and was therefore able to play on the sentiments of others. Perhaps the whole meaning of this poem is summed up in the last line, "So strong you thump O terrible drums--so loud you bugles blow." This and the last line of the first stanza are the only phrases of the poem that are not compulsory or inciting. Here, we are able to see a bit of Whitman break through the persona he has drawn up in order to embody. His method of persuasion in this poem is not only well thought out, but is commendably executed.