Final answer:
The availability of job opportunities in Northern cities was primarily responsible for the change in urban population during the early 20th century.
Step-by-step explanation:
The condition in society that was primarily responsible for the change in urban population was the availability of job opportunities in Northern cities. During the early 20th century, many people from rural areas and Southern communities moved to Northern cities in search of employment. The booming industries in cities like New York, Chicago, and Detroit offered jobs in factories and manufacturing, attracting a large influx of people seeking better economic opportunities.
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