The first evidence that Central European Jews migrated eastward (and eventually met up with other existing communities of the east, such as the East-Slavic Jews) comes from the 11th century. Some historians have claimed that the chronicler Cosmas of Prague wrote about Jews migrating from Bohemia into Poland, but the actual text merely says that some Jews fled and other transferred their property into Poland and Hungary, and there are no other details provided by Cosmas. But this idea was confirmed by the research of the onomastician Alexander Beider, who showed (using actual documents) in his book A Dictionary of Ashkenazic Given Names that many of the first Jews in Poland had Slavic given-names typical of those found in Bohemia and Moravia (now known as the Czech Republic). The same was true of the Jews living in eastern Germany in the 11th-13th centuries. In later years, many German Jewish families with Germanic names were added to the mix. Their descendants hold surnames like Shapiro (indicating their heritage in Speyer, Rhineland Germany), Mintz (from Mainz, Germany), Frank (from Franconia), Katzenellenbogen, Bachrach (from Bacharach, Rhineland Germany), Landau (from Landau, Rhineland Germany), Auerbach, Halperin, Ginsburg, Hammerstein, Frankfurter (from Frankfurt, Germany), Wiener (from Vienna, Austria), and Fischel (from Nürnberg, Germany), though not all bearers of the name Frank come from Franconia. Horowitz (= Gurevich) also comes from Central Europe and, before that, from Italy. The surname Teplitz also indicates roots in the Czech lands. The west-to-east migrations from Germany and Austria are confirmed by a number of authentic documents. For example, rabbis Israel Isserlein from Austria and Moses Mintz from Germany wrote in the 15th century that the Polish state of Krakow had for many years been a place of refuge for expelled Jews from Germany (see Bernard Weinryb, The Jews of Poland, 1973, pages 29-30).
By the 16th century, Ashkenazic given names from Central Europe - like Lipman, Golda, Tolba, Liber, Yenta, Zel'man, Perelo, Yuta, Mendel', Leyzar, and Kopel'man - were in common use among Jews throughout the Grand Duchy of Lithuania, including its component regions Lithuania, Belarus, and Volhynia (see Alexander Beider, A Dictionary of Ashkenazic Given Names, 2001, pages 195-196). This shows that a very significant part of the Jewish population of eastern Europe consisted of Jews from central Europe.
There were a small number of Jewish refugees from France who arrived in Hungary, as I mentioned in Chapter 11 of my book in the section "Jews in Hungary", but overall French Jews have no connection to the vast majority of Eastern European Jews.
Some Ashkenazic Jews have surnames indicating their ancestors came from Italy. An example is Luria (Lurie), which shows that the family originated in the Italian town of Lurinza.
Some Sephardic Jews from Spain, Portugal, and Turkey also found their way to Poland and Romania and intermarried with Ashkenazic Jews. This has been confirmed by investigating numerous individual families' genealogies, some of which have Sephardic surnames and oral traditions of Sephardic ancestry. The Rappaport families came from northern Italy to eastern Europe, but one theory contends that they originated in Oporto, Portugal. Other Sephardic surnames include Algazi and Basson. The existence of Sephardic Jews in Poland and Russia is briefly cited in the famous genealogy books by Dan Rottenberg (Finding Our Fathers) and Arthur Kurzweil (From Generation to Generation). An example of a town where Sephardic Jews settled is Zamosc in Poland.
The majority (over 50%) of Jews in Poland descend from German, Moravian, and Bohemian Jews, as I state on pages 282 and 289 in my book, The Jews of Khazaria. Page 289 reads, in part, "The Jewish populations in Poznan, Kalisz, Krakow, and Wroclaw were probably in the main descended from German, Moravian, and Bohemian Jews." However, I also think that the Khazarian Jewish elements are worth studying. Only by studying both the Western Jewish and the Khazarian Jewish ethnic contributions can be we completely objective. Weinryb's book confirms my assertion that Krakow and Wroclaw were major areas of settlement for Western Jews. Separate research by other prominent historians and linguists had led us astray into thinking that the early Jews of Kiev and Chernigov may have descended largely from the Khazars.
Kevin Alan Brook is the author of The Jews of Khazaria, the most recent general history of the Khazars in English. For additional documentation about the Western/Central European Jewish contribution to Eastern European Jewish demographics, consult his article "The Origins of East European Jews" in Russian History/Histoire Russe volume 30, numbers 1-2 (Spring-Summer 2003), pages 1-22.
Are Russian Jews Descended from the Khazars?