This document discusses several factors that contributed to rapid urbanization and population growth in U.S. cities between 1840-1860, including a booming agricultural economy in the West, improvements in public health, and large-scale immigration from Germany and Ireland. It also describes the rise of anti-immigrant nativist groups like the Native American Party and Know-Nothings during this period. Additionally, it summarizes the development and expansion of transportation networks like canals, railroads, and telegraph lines across the country during the mid-19th century.