Answer:
A confluence of factors rendered city life more attractive and feasible at the late nineteenth century.
Technology including electricity and telecommunications encouraged companies to grow and expand in towns, and skyscrapers allowed comparatively small geographical areas to continue to grow.
The growing need for workers has prompted a large influx of unemployed people both from the United States ' rural areas and Eastern and Southern Europe.
Urban housing, and also infrastructure including transportation and hygiene, has increased accordingly, while cities have struggled to cope with the rising demand.
Overall, technological advancements and a booming population contributed to American cities rising as never before.