As Brooklyn, the Bronx and Queens were sequentially linked to Manhattan through better transportation and political consolidation, the townhouse expanded to other districts. Speculative builders place row after row, varying the size (2, 3 or 4 floors), the number of exterior ornaments, and the quality of the interior finish to suit a particular neighborhood market. This row development began earlier and spread further into Brooklyn, the district best served by streetcar lines. It wasn't until the 1920s that apartment buildings were constructed so frequently.
The popularity of townhomes for everyone, except for the lowest income levels, is easy to explain. It provided many of the assets of a single-family home with privacy, gardens and capital, but at a lower price than single-family homes due to protomassive construction methods and efficient land use. Many people also appreciated the communal aspects of the townhouse, as the neighbors were shared in the backyards and on the front stairs. When these neighborhoods were developed in the late 19th and early 20th centuries, independent houses were built because land and construction were relatively cheap and market demand was strong.