Within half a century of its founding in 1833, Chicago, Illinois, became the second largest city in the United States, thanks to its location at the hub of the nation's growing railroad network. A center of manufacturing and commerce, Chicago attracted millions of transnational and American migrants during the nineteenth and twentieth centuries. As an exporter of products and ideas, Chicago influenced how Americans lived, and it served as an exemplar for those who thought about what a city was. Toward the end of the twentieth century, however, Los Angeles's automobile-oriented population outstripped Chicago's, dropped the “second city” to third in rank, and replaced it as the paradigm of urban form.