If by "suburb" is meant an urban margin¹ that grows more rapidly than its already developed interior, the process of suburbanization²（郊区化） began during the emergence³ of the industrial city in the second quarter of the nineteenth century.

Before that period the city was a small highly compact cluster（群，蔟） in which people moved about on foot and goods were conveyed by horse and cart. But the early factories built in the 1840's were located along waterways and near railheads（铁路末端） at the edges of cities, and housing was needed for the thousands of people drawn⁴ by the prospect⁵ of employment. In time, the factories were surrounded by proliferating⁶（增生的） mill towns of apartments and row houses that abutted⁷（毗邻） the older, main cities. As a defense⁸ against this encroachment⁹（侵入） and to enlarge their tax bases, the cities appropriated their industrial neighbors. In 1854, for example, the city of Philadelphia annexed¹⁰ most of Philadelphia County. Similar municipal maneuvers¹¹（军事演习） took place in Chicago and in New York. Indeed, most great cities of the United States achieved such status only by incorporating the communities along their borders.

With the acceleration¹² of industrial growth came acute urban crowding and accompanying social stress-conditions that began to approach disastrous¹³ proportions when, in 1888, the first commercially successful electric traction¹⁴ line was developed. Within a few years the horse-drawn trolleys¹⁵（手推车） were retired¹⁶ and electric streetcar networks crisscrossed and connected every major urban area, fostering a wave of suburbanization that transformed the compact industrial city into a dispersed¹⁷（分散的） metropolis¹⁸. This first phase of mass-scale suburbanization was reinforced by the simultaneous emergence of the urban Middle Class, whose desires for homeownership in neighborhoods far from the aging inner city were satisfied by the developers of single-family housing tracts¹⁹.