I think that Sandburg is speaking to a people who is enduring a monumental struggle during the Great Depression. In one of the most unspeakable times in American History in terms the toll it took on Americans, the cost in both finances and human life, and the overall psychological malaise that gripped Americans, Sandburg offers the following line in his work:
We are the greatest city, the greatest people. Nothing like us ever was.
Consider the power of such words in the most dire of times. There is a power of hope that is present in what Sanburg is saying to the reader, to those who struggled with life during the Great Depsression. Sandburg understood the need for inspiring absolute hope in the most dire of situations and did so in seeking to articulate the nature of American character that is present in the zenith of our successes and the valleys of our experience. To this end, Sandburg is speaking about the struggles being endured, and how they are only reflective of the national character of America.