As the new nation came of age, discontent in Europe created immigrant patterns from Ireland and Germany that peaked in the 1850s with millions of new Americans.
The first great wave of immigration began in the 1820s during a period in American history that witnessed expansion, innovation, and the beginning of a modern society. The United States offered hope with the prospect of prosperity and security for many Europeans struggling with the post Napoleonic period. Although thousands came from the British Isles, this first great migration of immigrants represented the Irish and the Germans.
Irish Immigration Patterns in the Early 19th Century
The great potato blight in Ireland created intolerable living conditions as famine swept the land and the British Parliament refused to address the problem. With few options, the Irish crossed the Atlantic by the hundreds of thousands, arriving either in Canada or port cities in the Northeast such as Boston. Unlike the German and Scandinavian immigrants of the same period, the Irish were unskilled and thus forced to find employment near the large northern urban centers.
Irish immigrants helped build the new nation’s infrastructure and ultimately contributed significantly to the Union’s cause during the Civil War. Mass Irish immigration also introduced a broader presence of Roman Catholicism. Although Catholics had a presence in America since the Maryland colony was founded in 1634, by 1838 there were over 800,000 Catholics in the United States led by twelve bishops and 433 priests. 
German Immigrants in the Early 19th Century
German immigrants were skilled craftsmen and farmers, coming from Middle Germany in the late 1840s and 1850s. Settling in states like Missouri and Illinois, Germans fled Europe in the wake of the Revolutions of 1848. German-Hungarians, for example, settled by the Empress Maria Theresa in the mid-1700s on the Hungarian frontier, moved to the Chicago area. Many of the German immigrants also brought Catholicism to America.
Earlier German immigrants during the Colonial period had been predominantly Protestant. Members of Pietistic groups like the Moravians, Amish, and Mennonites had settled in Pennsylvania and were known as “Pennsylvania Dutch,” a misnomer attributed to the German word Deutsch (meaning “German”). In the early 1700s, Germans could also be found in the Carolinas and Georgia, notably near Savannah. German contributions during the American War for Independence were many and large numbers of British mercenary soldiers such as the Hessians either stayed when the war ended or made provision to return as immigrants.
Reception of Immigrants by American Society in the 19th Century
The arrival of so many immigrants created massive problems in Northern cities. The Five Points district in New York City spawned the cholera outbreak during the presidency of Andrew Jackson which led to stereotyping immigrants by middle class and wealthy Americans. Emerging slums further exacerbated sanitation concerns and produced irrational fears. Xenophobia caused a backlash, especially against the Irish.
By the 1850s, strong nativist feelings led to the formation of the American party, often referred to as the “Know-Nothings.” Believing that low-wage earning immigrants would take away jobs and fearful of the perceived authoritarianism of Catholicism, Know-Nothings attempted to pass strict laws restricting immigrants. No Catholics, for example, could run for office in those jurisdictions controlled briefly by the nativists.
Legacy of the First Great Immigration Migration
Both Irish and German immigrants helped forge the new nation precisely at a time when innovation, creativity, and labor were needed. Germans like Horace Mann in the 1830s and 1840s reformed American education. Carl Schurz, a founder of the Republican Party and a refugee of the 1848 Revolutions in Europe, became a national leader, championing Abraham Lincoln, crusading for party reform after the Civil War, and strongly opposing American imperialism at the turn of the century.
Similarly, Irish immigration produced men and women that would lead the nation. President John F. Kennedy could trace his roots back to the first wave of Irish immigrants coming to Massachusetts. Immigrants made the United States a nation “out of many.”
-  See Page Smith, A Nation Comes of Age (McGraw Hill) (chapter on immigration)
- Roger Daniels, Coming to America: A History of Immigration and Ethnicity in American Life, 2nd Ed. (New York: Harper Collins, 2002)