Between 1776 and 1882, tens of millions of immigrants left their homelands—overwhelmingly from locations in Europe—to build new lives in the United States. They came in geographically-specific waves—first from England, then from Ireland and Germany, still later from Southern and Eastern Europe.
These patterns cannot be explained as the simple aggregate of tens of millions of individual choices, made by migrants pulled to New World by the lure of American economic opportunity. Vast macroeconomic forces were also at work, pushing migrants out of their home countries.
We have a name for those forces: the Industrial Revolution. The Industrial Revolution was always accompanied by a revolution in agricultural production. By adopting new crops and new technologies, farms were able to produce more food with fewer workers. In one sense, this was progress—millions of peasants were freed from a lifetime of backbreaking rural labor. In another sense, though, this was a problem—millions of peasants were freed from the only work they had ever known, and needed to find new forms of employment.
If they couldn't find work on the farm, they migrated to town; if they couldn't find work in town, they migrated to Europe's teeming cities; if they couldn't find work in Europe's teeming cities, they migrated abroad.
In the nineteenth century, Europe's population doubled, from 200 to 400 million, and another 70 million people emigrated to other continents. Half of those came to the United States, while Canada, Australia, and South America also welcomed millions of newcomers.21
Waves of immigration to America tended to correspond less to changing policies or circumstances within the United States than to the timing of the arrival of the Industrial Revolution in the countries of origin. The Industrial Revolution came first to England, in the late eighteenth and early nineteenth century, prompting heavy English immigration to the United States during that period. By the middle of the nineteenth century, the Industrial Revolution reached Ireland and Germany, and throngs of Germans and Irishmen poured into Boston and New York. And when the Industrial Revolution finally reached Eastern and Southern Europe in the last years of the nineteenth century, America received "the New Immigration" of Italians, Poles, Jews, and Slavs. The same basic forces are at work today in much of Latin America and Asia, driving contemporary patterns of immigration into this country.
Not all causes of immigration were economic, of course. Political turmoil, such as that which afflicted France in the 1790s and much of Europe in 1848, created refugees who frequently found their way to American shores. So too did crop failures and famines, such as those which struck Ireland in 1845 and China in 1852. But these emergency migrations were the exception rather than the rule.
For foreigners driven from their homelands and forced to seek work abroad, the United States was an alluring destination. The American economy grew at a robust rate throughout much of the nineteenth century, offering workers higher wages than prevailed in Europe. And America had land! Few Europeans could realistically hope to own their own land in their home countries, but land on the American frontier was abundant. After the passage of the Homestead Act in 1862, the U.S. government literally gave land away for free; anyone willing to make improvements and occupy a plot of land in the west for five years could receive title to a 160-acre stake. The Homestead Act was passed with the interests of native-born Americans in mind, but word soon spread to Europe, where it inspired even higher rates of migration to the United States.