Jewish communities have existed for long periods of time in regions throughout the world. While Judaic or Hebraic have long been considered discreet ethnic designations, the fact that one's Jewishness has more to do with religious belief than genetic history has confused this label over the centuries. It has been nearly 2000 years since Jews belonged to a single ethnicity, a result of the great Jewish Diaspora that followed the Jewish rebellions against Roman rule in the imperial province of Judea. When Jerusalem was sacked and the Jews still living in the Roman Empire were scattered across the globe, smaller Jewish communities flourished outside of the once sovereign territory of Canaan. By the Middle Ages, three major ethnic subgroups arose within the Jewish community and we still recognize those groups today. They are the Ashenazim, the Sephardim and the Mizrahim.
Ashkenazi Jews made their home in the Rhine region, what is today Germany and much of Central and parts of Eastern Europe. The term "Ashkenaz" is the Medieval Hebrew word for German or Germanic. For a long time, the Ashkenazim were the smallest Jewish ethnic group, owing to a lack of material prosperity and general social isolation. By the 19th century, the Ashkenazim were the largest group of Jews in the world, their tight communities making marriage outside the faith difficult and their strong sense of identity creating a very distinct culture. Between the 19th and 20th centuries, millions of Ashkenazim immigrated to the United States seeking refuge from the oppression of antisemitic governments like Russia under the Czars and the fascist governments of Germany and Austria. Today, most American Jews have a clear Ashkenazi heritage, which includes Eastern European style food, the Yiddish language and the Roma-inspired Klezmer music genre.
Sephardic Jews are those who come from a Western and sometimes Northern European background. This was a particularly large Jewish ethnic group in the Middle Ages, thanks mostly to the presence of Muslim powers in Iberia. While Jews in the Middle Ages regularly suffered through expulsions (especially in England) and oppression under the famed Inquisition in Portugal, Spain and France, Muslim rulers in Spain and North Africa tended to be more tolerant of foreign faiths. As the Industrial Revolution and the increased secularization of Western Europe made life more hospitable for Jews, many of the Sephardim who had not already converted to other faiths further integrated into regular society. Where once the Western cities of what the Jews called "Spharad" were home to the greatest scholars of the faith, the Sephardim were forced by political circumstances to scatter several times throughout their history. Large groups went to Brazil, the United States and Israel, bringing with them the cultural hallmarks of Western Europe and a take on Jewish liturgy that differs somewhat from the Ashkenazi concepts most Jews adhere to today.
Mizrahi Jews are those who remained or eventually resettled the East after the diaspora. Their region includes a far-flung collection of locales including Israel, parts of Africa, the Caucasus Mountains and even India and Pakistan. This placed them almost entirely within Muslim-dominated societies, with varying results throughout history. More ethnically distinct than their Sephardic cousins but not as socially isolated as the Ashkenazim, the Mizrahi Jews survived much as their ancestors did, as a combination of landed provincial people and creative urban professionals. Many recent controversies, especially the ongoing Arab/Israeli conflict, has pushed most Mizrahim to immigrate to Israel, though many of North African origins made large communities in France.
Today, the ethnic subgroups of Jewish culture aren't as strongly defined as they once were. There is such a thing as a global Jewish community now, made possible by communications technology and a center of heritage in Israel. Jews are a well-traveled people, though thankfully modern social progress has allowed Jews to thrive without having to survive in ethnically isolated communities.