In 1860, fewer than 13 percent of Americans lived in urban areas and only nine cities could claim 50,000 or more residents. Thirty years later, however, the urban population was soaring. By 1898, 30 percent of Americans were city dwellers, and Kansas City, Minneapolis, and other midwestern cities grew by more than 1,000 percent.
Rising population and the growth of businesses sent mail volume to new heights. The cities thrived on commerce, and the lifeblood of commerce was the U.S. mail. By 1900, the Post Office Department was serving citizens scattered sparsely over vast territories and millions crowded together within a few square miles.