Human mobility has its own periodization and its own geography. Neither tracks neatly to the more familiar periodization of American domestic politics or the geography of US international relations. While presidential elections, regional conflicts, and international treaties may influence mobility, their precise impact is not always predictable. Migration, developing in tandem with commerce, war, diplomacy, and the movement of capital investment, is always part of globalization, defined here as result of waxing and waning networks of diverse transnational circuits.

Viewing US immigration as one element in a history of globalization pushes attention away from a nineteenth century that began in 1800 and ended in 1899 toward a “long nineteenth century” that began and ended somewhat later. The United States first reported data on migrants in 1820; after 1840 immigration regularly surpassed one million entries per decade. (That means that in the 1840s each year of immigration added 0.6 percent to the American population.)