In "Beat! Beat! Drums!" we get a nice glimpse into the lives of American people. In the eyes of our speaker, the United States is a land made up of scholars, church-goers, and people who are used to going about their business, working hard. But at this moment in time, our speaker's vision of America is disrupted: this is now a country at war. It's easy to see how such a clear vision – an image that seems like a simple slice of American life – can be totally skewed by a civil war.
The poem describes a wide variety of people – from brokers to farmers, children to mothers, scholars to sleepers – to show that every citizen, regardless of position, age, or gender, is affected by the terrible build up to the Civil War.
Our speaker tends to identify people by the work that they do. Nothing ever changes: even today, Americans are a people largely defined by their work.