Economic expansion fueled a demand for labor, which was met, in part, by increased immigration from abroad. Between 1790 and 1830, immigrants contributed only marginally to American population growth. But between 1840 and 1860, over 4 million people (more than the entire population of 1790) entered the United States, the majority from Ireland and Germany. About 90 percent headed for the northern states, where job opportunities were most abundant and the new arrivals would not have to compete with slave labor. Immigrants were virtually unknown in the slave states, except in cities on the periphery of the South, such as New Orleans, St. Louis, and Baltimore. In the North, however, they became a visible presence in both urban and rural areas. In 1860, the 814,000 residents of New York City, the major port of entry, included more than 384,000 immigrants, and one-third of the population of Wisconsin was foreign-born.
Numerous factors inspired this massive flow of population across the Atlantic. In Europe, the modernization of agriculture and the industrial revolution disrupted centuries-old patterns of life, pushing peasants off the land and eliminating the jobs of traditional craft workers. The introduction of the ocean-going steamship and the railroad made long-distance travel more practical. The Cunard Line began regular sailings with inexpensive fares from Britain to Boston and New York City in the 1840s. Beginning around 1840, emigration from Europe accelerated, not only to the United States but to Canada and Australia as well. Frequently, a male family member emigrated first; he would later send back money for the rest of the family to follow.