The Jewish population of the U.S. is the product of waves of immigration primarily from diaspora communities in Europe; emigration was initially inspired by the pull of American social and entrepreneurial opportunities, and later was a refuge from the peril of ongoing European antisemitism. Few ever returned to Europe, although committed advocates of Zionism have made aliyah to Israel.
America's appeal as an easy-to-enter "melting pot" for many cultures led to a new commonality of culture and political values. This open culture allowed many minority groups, including Jews, to flourish in Christian and predominantly Protestant America. Antisemitism in the United States has always been less common than in other historic areas of Jewish population, whether in Christian Europe or in the Muslim parts of the Middle East .
From a population of 1,000–2,000 Jewish residents in 1790, mostly Dutch Sephardic Jews, Jews from England, and British subjects, the American Jewish community grew to about 15,000 by 1840, and to about 250,000 by 1880. Most of the mid-19th century Ashkenazi Jewish immigrants to the U.S. came from diaspora communities in German-speaking states, in addition to the larger concurrent indigenous German migration. They all initially spoke German, and settled across the nation, assimilating with their new countrymen; the Jews among them commonly engaged in trade, manufacturing, and operated dry goods (clothing) stores in many cities.
Between 1880 and the start of World War I in 1914, about 2,000,000 Yiddish-speaking Ashkenazi Jews immigrated from diaspora communities in Eastern Europe, where repeated pogroms made life untenable. They came from Jewish diaspora communities of Russia, the Pale of Settlement (modern Poland, Lithuania, Belarus, Ukraine and Moldova), and the Russian-controlled portions of Poland. The latter group clustered in New York City, created the garment industry there, which supplied the dry goods stores across the country, and were heavily engaged in the trade unions. They immigrated alongside indigenous eastern and southern European immigrants, which was unlike the historically predominant American demographic from northern and western Europe; Records indicate between 1880 and 1920 that these new immigrants rose from less than five percent of all European immigrants to nearly 50%. This feared change caused renewed nativist sentiment, the birth of the Immigration Restriction League, and congressional studies by the Dillingham Commission from 1907 to 1911. The Emergency Quota Act of 1921 established immigration restrictions specifically on these groups, and the Immigration Act of 1924 further tightened and codified these limits. With the ensuing Great Depression, and despite worsening conditions for Jews in Europe, with the rise of Nazi Germany, these quotas remained in place with minor alterations until the Immigration and Nationality Act of 1965.
Jews quickly created support networks consisting of many small synagogues and Ashkenazi Jewish Landsmannschaften (German for "Territorial Associations") for Jews from the same town or village.
Leaders of the time urged assimilation and integration into the wider American culture, and Jews quickly became part of American life. During World War II, 500,000 American Jews, about half of all Jewish males between 18 and 50, enlisted for service, and after the war, Jewish families joined the new trend of suburbanization, as they became wealthier and more mobile. The Jewish community expanded to other major cities, particularly around Los Angeles and Miami. Their young people attended secular high schools and colleges and met non-Jews, so that intermarriage rates soared to nearly 50%. Synagogue membership, however, grew considerably, from 20% of the Jewish population in 1930 to 60% in 1960.
The earlier waves of immigration and immigration restriction were followed by the Holocaust that destroyed most of the European Jewish community by 1945; these also made the United States the home for the largest Jewish diaspora population in the world. In 1900 there were 1.5 million American Jews; in 2005 there were 5.3 million. See Historical Jewish population comparisons
On a theological level, American Jews are divided into a number of Jewish denominations, of which the most numerous are Reform Judaism, Conservative Judaism and Orthodox Judaism. However, roughly 25% of American Jews are unaffiliated with any denomination. Conservative Judaism arose in America and Reform Judaism was founded in Germany and popularized by American Jews.