You can feel Emily’s frustration at getting involved between the argument of two friends, one of which turns on her for interfering, and which ultimately leads to her wanting to just shoot everyone, herself included, to be done with this nonsense. We never learn what the friends are quarreling about, but it must be something petty – which is interesting because it escalates into tragedy.
The difference between tragedy and comedy is that in a comedy the characters are usually unaware that their actions (their shortcomings) are the cause of their failures, while in a tragedy the characters are painfully aware (at least by the end of the story) that their shortcomings are leading to their failure yet they are unwilling to do anything to prevent the tragic outcome.
In this poem Emily sees both the comedic and the tragic qualities of getting involved in an argument between friends. At first she is more than happy to just watch this “Battle picturesque” as one “friend attacks” the other “friend”. The word “picturesque” is worth digging into because it doesn’t just mean a pretty scene that is “pleasing or striking in appearance; scenic” (OED), it can also be used figuratively to describe something “strikingly graphic or vivid, colorful; (ironically) careless of the truth, esp. for effect”, such as a line Jack London writes in Sea Wolf, “For the first time in my life I experienced the desire to murder—‘saw red’, as some of our picturesque writers phrase it” (emphasis mine). Thus the use of this word hints at the possibility that the friends are bickering over something trivial or are having a simple misunderstanding.
However, Emily gets involved by line three, “Then I turn Soldier too”. We don’t know why she has jumped in, but perhaps she has because she thought the issue could be easily solved since it seemed so petty to her as an observer. There isn’t a line break or a dash leading into line three (in fact the poem is devoid of her unusual punctuation), rather she just jumps right in assuming she will find a solution to the issue. Yet in line four one of her friends – and she carefully chooses not to say which one because it could as well be either of them – turns on her and mocks her for getting involved. It might also be worth noting that she uses then pronoun “he”, not ‘she’ or ‘her’ so she might be writing about her frustrations at dealing with pig headed men who refuse to back down from an argument with each other and will turn on anyone who tries to get in the way. Not that women aren’t equally guilty of being stubborn in an argument, but she is equating this poem’s military and war imagery (“attack”, “Battle”, “Soldier”, “martial”, “gun”, “shoot”m and “glory”) with a male pronoun.
The final four lines of the poem are pure frustration with the situation she finds herself in which she expresses nicely with hyperbolic image of a gin so large she could shoot everyone, including herself, and just be done with it all. Thus in the end she combines the comic aspects of the poem with a tragic ending in which everyone dies. And I think this is important because I wonder if we think of the argument between her two friends as a political argument between the situation going on in the United States at the time. Many people in the north, especially in New England, believed they had the moral high ground concerning the issue with the South, but there were many people in the North who benefited from the South’s exploitation of slaves. Arguments over what to do in the lead up to the US Civil War would eventually become brother fighting brother on the battlefield during the war. Thus this poem seems to predict the tragedy and the comedy of the political situation in America at the time, especially the ending which sees the issue resolved with extreme violence.
In fact, if she did perhaps have the political climate in mind when she wrote this, we can feel her exasperation with the situation in that she feels totally powerless to bring about a resolution to an argument she sees as about to turn tragic in a comically awful way. And I’m not saying there is anything funny about the US Civil War or that she was making light of it, I’m using comedy in the darker sense like the way the film Dr. Strangelove looks at the tragedy of impending doom through the lens of a comedy in which everyone involved is an idiot – a dangerous and armed idiot.