Final answer:
During the nineteenth century, U.S. cities faced numerous issues including fire, crime, and disease. However, unemployment was not a significant problem by the end of this century due to prosperity following World War I, specifically marked by mass production spurring job growth.
Step-by-step explanation:
The student has queried about what was not a problem in most U.S. cities during the nineteenth century.
Considering the historical context of the time, the presence of fire, crime, unemployment, and disease were in fact significant issues that plagued urban areas due to rapid industrialization and urbanization.
Cities like New York and Chicago struggled with these challenges due to dramatic population increases and the stresses that came with it. However, based on data from the period of prosperity following World War I, where mass production and the availability of jobs led to a distinct drop in unemployment rates, it can be posited that unemployment was not as much of a dire problem by the end of the nineteenth century.