Final answer:
By 1960, half of the American population lived in metropolitan areas, which represent a broader urban environment including suburbs around cities. This was part of a wider trend throughout the 20th century where urbanization increased due to industrialization, technological advancements, and immigration.
Step-by-step explanation:
The question pertains to the demographic changes in the United States over the 20th century with a focus on urbanization. To answer the student's question: by 1960, 40 years after more than half the American population lived in urban places, half of the population lived in metropolitan areas, which include the suburbs around cities.
During the late 1800s, the United States experienced a rapid population growth, much of which took place in urban areas. This shift was largely fueled by the Industrial Revolution and the subsequent concentration of manufacturing in cities. By 1920, about 50 percent of the population lived in cities, and as time went on and the economy developed, an increasing proportion of the population began living in metropolitan areas.
By the second half of the 20th century, the trend of urbanization continued, and manufacturing also began to move to rural areas. However, up until that point, it was almost exclusively an urban activity. Factors that have contributed to urbanization include industrialization, the development of commercial electricity, and immigration—all of which helped transform American society from primarily rural to significantly urban.