It took a long time to rebuild. In the 18th and 19th centuries, Harlem developed slowly compared to the rest of Manhattan. Initially rural, with large estates and farms, it became a retreat for wealthy landowners. Infrastructure improvements, especially the New York and Harlem Railroad, spurred development in the mid-1800s, transforming Harlem into an industrial suburb. Wealthy land speculators, like Charles Henry Hall, helped modernize the area. Over time, Harlem's population diversified, including Irish squatters, poorer Jewish, and Italian immigrants, especially after the Civil War, leading to significant economic growth.