Industry and trade dramatically affected the growth of cities in the period before World War I in which the United States was rapidly industrializing.  Mostly, industry and trade combined to make big cities bigger and to reduce the size of some smaller towns.

With the boom in industrialization in the late 1800s, the biggest cities got much bigger.  This was more possible now because railroads could bring in the raw materials needed for industry and could take out the finished goods.  For example, Chicago got much bigger in part because it became the center of the meat-packing industry.  Pittsburgh grew as the center of the steel industry.  The big new factories and the extensive railroads made cities even bigger magnets for jobs and residents than they had once been.

By contrast, smaller country towns typically became smaller or disappeared altogether.  There was much less need for scattered urban centers now that there was better transportation and more industry.  These smaller towns lost much of their economic purpose and often withered, particularly if they were not on railroad lines.

Thus, industry and trade had a great impact on the growth of cities in this time.