If by "suburb" is meant an urban margin that grows more rapidly than its already developed interior， the process of suburbanization began during the emergence of the industrial city in the second quarter of the nineteenth century. Before that period the city was a small highly compact cluster in which people moved about on foot and goods were conveyed by horse and cart. But the early factories built in the 1830's and 1840's were located along waterways and near railheads at the edges of cities， and housing was needed for the thousands of people drawn by the prospect of employment. In time， the factories were surrounded by proliferating mill towns of apartments and row houses that abutted the older， main cities. As a defense against this encroachment and to enlarge their tax bases， the cities appropriated their industrial neighbors. In1854， for example， the city of Philadelphia annexed most of Philadelphia County. Similar municipal maneuvers 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 acceleration of industrial growth came acute urban crowding and accompanying social stress —— conditions that began to approach disastrous proportions when， in 1888， the first commercially successful electric traction line was developed. Within a few years the horse-drawn trolleys were retired and electric streetcar networks crisscrossed and connected every major urban area， fostering a wave of suburbanization that transformed the compact industrial city into a dispersed metropolis.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 tracts.
郊区的发展 如果"郊区"指的是比已建好的城市内部发展更为迅速的城市边缘地带，那 么郊区化可以说始于 1825 年至 1850 年工业化城市出现期间。
在这之前，城市只是高度密 集的小聚居群。 在其中，人们步行走动，商品靠马车来运送。 但是建于 18 世纪三四十年 代的早期工厂位于城边的航道和铁路附近，被工作机会吸引到这里的成千上万的人们需要住房。 渐渐地，在与旧有的主要城区相毗邻的地方，不断涌现出由排房和公寓楼组成的工人聚居区，包围了工厂。作为对这种侵蚀的自卫，也为了扩大它们收税的地域范围，城市吞并了工业化的临近地带，比如 1854 年费城的城区就兼并了费县的绝大部分地区。相似的城市 化也发生在芝加哥和纽约。今天很多美国的大城市其实就是靠吞并它们附近的边缘地区而 变成大都会的。随着工业化的加速发展，城市里出现了严重拥挤和相伴而来的社会压力。 当1888 年第一条商业上成功的电气化铁轨被制造出来时，压力开始接近危机的程度。 几年之内，马车就被废弃了，电车网相互交织连接着各个重要的城区，从而形成了一种郊区化的潮 流，即密集的工业城市转变成了分散的都市。
此时城市中产阶级的出现进一步加强了第一 波大规模郊区化。 这些中产阶级希望在远离老旧城市的地区拥有住宅，单一家庭住宅地区 的开发者满足了他们的愿望。