Between 1870 and 1920, around 20 million European immigrants arrived in the US, primarily from eastern and southern Europe. They came to escape persecution, improve their economic prospects, and experience greater freedom. Most settled in northeastern and midwestern cities, where over half the populations of major cities were immigrants by 1910. Urbanization brought challenges around housing shortages, sanitation issues, and the rise of political machines that sometimes engaged in corruption. Reformers established settlement houses to help immigrants adapt to urban life.