In Chapters 12 and 13 of America: Past and Present by Robert Divine, which factors were most important in pushing or pulling great waves of immigrants to the United States between 1820 and 1850?
Arguably. the greatest wave of immigrants arriving in the United States was the nearly one million Irish who came after the Great Famine of the 1845. After Napoleon was defeated in France in 1815, travel restrictions were loosened and nearly 150,000 European immigrants arrived. Then, as Europe seemed to be getting more crowded and many people were displaced, by the 1830s nearly 600,000 arrived in New York City. By the 1840s, the numbers increased to nearly 1.7 million. However, the largest number of immigrants arrived during the 1850s: approximately 2.6 million, among whom so many were starving Irish, but many others were Germans, who fled because of an economic depression; others were Jewish who came to America, fleeing growing anti-Semitism in Europe. Those from Poland and Russia fled bloody pogroms; they increased from three thousand in 1818 to one hundred fifty thousand in 1850. Also in this largest of numbers in the middle of the nineteenth century were the Scandinavian immigrants from Denmark, Norway, and Sweden, adventurous people who also fled "persecution or discrimination rooted in religious intolerance." With many who were farmers, they settled in Minnesota, Iowa, and North Dakota. (In fact, Minnesota is the Norwegian capital of the United States.) In addition to economic, political, and religious reasons--hunger or persecution--there was always, too, the enticement of opportunity and the possibilities of a free society that drew many immigrants to the expansive new country.
During the period from 1840 to 1860, over four million European immigrants came to the United States, mainly from Ireland and Germany. Divine notes the pull factor of available jobs, as European immigrants were needed in the 1820s–1850s to fill the hundreds of thousands of jobs that were created by industrialization. The Industrial Revolution fueled the growth of the factory system, particularly in the northeast, where the development of industry, transportation, and agriculture spurred economic growth and created the need for workers. The push factors driving immigrants to come to the United States included poverty and famine, most notably the potato famine in Ireland. Immigrants had few opportunities in Europe and came to the United States in search of higher-paying jobs. They ironically took low-wage jobs, mainly in port cities, after arriving in the United States. The Irish in particular faced poverty, including poor urban living conditions, and they faced discrimination from native-born Americans.