Contrary to what some Americans seem to believe, the United States historically has been a polyglot nation containing a diverse array of languages. At the time of independence, non-English European immigrants made up one quarter of the population and in Pennsylvania two-fifths of the population spoke German.1 In addition, an unknown but presumably significant share of the new nation’s inhabitants spoke an American Indian or African language, suggesting that perhaps a third or more of all Americans spoke a language other than English. With the Louisiana Purchase in 1803 (which doubled the size of the country), the Treaty of 1818 with Britain (which added the Oregon Country), the Adams-Onís Treaty of 1819 with Spain (which gave Florida to the U.S.), and the Treaty of Guadalupe Hidalgo in 1848 (which acquired nearly half of Mexico), tens of thousands of French and Spanish speakers along with many more slaves and the diverse indigenous peoples of those vast territories were added to the linguistic mix.2 Alaska and Hawaii would follow before the end of the 19th century.
Although conquest clearly played a role in the 18th and 19th centuries, language diversity in the United States has been driven primarily by immigration. Germans and Celts entered in large numbers in the 1840s and 1850s, followed after the Civil War by Scandinavians in the 1870s and 1880s and then by Slavs, Jews, and Italians from the 1880s to the first decades of the 20th century. According to the 1910 census, which counted a national population of 92 million, 10 million immigrants reported a mother tongue other than English or Celtic (Irish, Scotch, Welsh), including 2.8 million speakers of German, 1.4 million speakers of Italian, 1.1 speakers of Yiddish, 944,000 speakers of Polish, 683,000 speakers of Swedish, 529,000 speakers of French, 403,000 speakers of Norwegian, and 258,000 speakers of Spanish.
Linguistic diversity began to wane with the cessation of mass European immigration, which ended abruptly in 1914 with the outbreak of World War I in 1914, revived somewhat afterward, but then lapsed into a “long hiatus” during which flows were truncated by restrictive U.S. immigration quotas, a global depression, a second world war, and ultimately the transformation of Europe into a zone of immigration rather emigration.3 As a result, the percentage foreign born fell steadily in the United States, going from 14.7% in 1910 to reach a nadir of 4.7% in 1970,4 at which point language diversity had dwindled to the point where the Census Bureau stopped asking its question on mother tongue.
Source: Immigration and Language Diversity in the United States – PMC
While immigrants arrive speaking their native tongue (and possibly also English), the use of their native language historically faded away during the next one or two generations. Even if kids learned their native language, their own kids tend not to master the native language.
Immigrants were pressured (or wanted) to “fit in” by speaking English. Schools would not permit children to converse in their native language. The consequence was that language skills faded away and rarely carried forward more than one or two generations (there have been some exceptions to that, of course).
One of my grandmother’s spoke Norwegian (I heard her speak Norwegian) but I never heard my Mom say anything in Norwegian nor say she knew Norwegian. We believe another grandmother spoke German or Swiss German (her parents were from Switzerland), and she appears to have translated some family letters and documents into English, but we never heard her speak German.
My Dad spoke some German, but I understand it was learned in school/college – and never heard him say he learned German from his mother (but I do not know). Because of his graduate education, and the university department requirements, he may have been required to know German at the B1 level – but we will never know the details. Both my parents have passed away.