If by "suburb" (1) 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 (2) compact cluster in which people moved (3) 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 at the (4) of cities, and housing was needed for the thousands of people (5) by the prospect of employment. (6) , the factories were surrounded by proliferating mill towns of apartments and row houses that abutted the older, main cities. As a (7) against this encroachment and to (8) their tax bases, the cities appropriated their industrial neighbors. In 1854, for example, the city of Philadelphia annexed most of Philadelphia County. Similar (9) maneuvers took place in Chicago and in New York. Indeed, most great cities of the United States (10) such status only by incorporating the (11) along their borders. With the (12) of industrial growth came acute urban crowding and accompanying social stress—conditions that began to (13) disastrous proportions when, in 1888, the first commercially successful electric traction line was (14) . Within a few years the horse- drawn trolleys were retired and electric streetcar networks crisscrossed and (15) every major urban area, fostering a wave of suburbanization that (16) the compact industrial city into a (17) metropolis. This first (18) of mass-scale suburbanization was reinforced by the (19) emergence of the urban Middle Class, whose desires (20) homeownership in neighborhoods far from the aging inner city were satisfied by the developers of single-family housing tracts.