Final answer:
The transition from an agricultural to an industrial economy contributed to the urbanization of the United States during the first half of the 20th century.
Step-by-step explanation:
The factor that contributed to the urbanization of the United States during the first half of the 20th century was the transition from an agricultural to an industrial economy. As industries grew and cities became centers of manufacturing and commerce, more people moved from rural areas to cities in search of jobs and better opportunities. This led to the development of urban areas and the expansion of cities.
Learn more about Urbanization in the United States