Between the late 19th and early 20th centuries, millions of immigrants from Europe, Asia, the Caribbean, and Mexico arrived in the United States, primarily settling in urban areas. They came for opportunities for work and to escape difficult conditions abroad. Immigrants faced harsh processing at arrival points like Ellis Island and Angel Island before trying to assimilate into American culture or creating ethnic enclaves. Rapid urbanization strained infrastructure and led to overcrowding, disease, and other problems as cities struggled to provide services for the large influx of newcomers. Political machines also exploited immigrants and the poor through corruption and graft.