Walt Whitman does something really neat with this poem: he gives us a glimpse into some very particular, individual moments, but he also zooms out so we can see the big picture. It's hard to keep both of those perspectives in mind when talking about war, but our poet manages to do it.
Time-wise, we're definitely in 1861 here: we've got a civil war going on in the Unites States, and it's just getting started. What's brilliant about this poem is that it gives us an idea of the calm that exists outside of wartime, and then throws it into complete chaos. Everyone – students, farmers, newlyweds, and even people who are sleeping – are totally disrupted by the war. We can imagine each of these people – lawyers who stop lawyering, mothers who hide their sons – and we feel for them.
And then we zoom out. When we hear the music rising over "cities" (plural), we get a sense of this force sweeping across all of America. We're not in one particular place here: now, even when we're dealing with a single person (a farmer, mother, or scholar), they seem to represent not just an individual, but a whole category of people (all farmers, mothers, or scholars). And that may be just the point the speaker is making: we must pay attention to the war because it's everywhere affecting everyone.