Many factors have been important in shaping the 20th-century American metropolis, and others will shape the city of the next century.
Immigration is a driving force behind many of the most important changes in the city.
Although it may not be as visible as the interstate highway system, this social force has had profound economic and physical impacts. Immigration is well recognized for its importance in building cities prior to 1920, but many experts and policy makers fail to perceive its continuing influence through the 1950s, its ebbing impact during the 1960s and 1970s, or its resurgence in the 1980s and '90s. The effect of immigration is to bring new residents to large cities, concentrating them in older gateway neighborhoods where they take root and invest their energies. The housing and retail markets at the heart of many of our large cities are sustained by these new arrivals. And the ready supply of willing workers encourages new job creation.