What is suburbanization If by "suburb" is meant an urban (47) that grows more rapidly than its already developed interior, the process of suburbanization began during the (48) of the industrial city in the second quarter of the 19th century. Before that period the city was a small highly (49) cluster in which people move about on foot and goods were (50) by horse and cart. But the early factories built in the 1830s and 1840s were (51) 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 (52) by proliferating mill towns of apartments and row houses that abutted the older, main cities. As a defense (53) this encroachment and to enlarge their tax base, the cities appropriated their industrial neighbors. In 1854, for example, the city of Philadelphia (54) most of Philadelphia County. Similar things (55) place in Chicago and in New York. Indeed, most great cities of the United States (56) such status only by annexing the communities along their borders.