Khazar Theory o hai there, anti-semites.
Have you heard of the Khazar Theory of Ashkenazic origins? I like to read blogs on human genetics, which seem to attract the occasional Neo-Nazi, and have Facebook friends who think bombing Palestine is a bad idea, which also attracts Neo-Nazis, so I’ve heard all about the Khazar Theory.
The one fact behind this theory: There was once a central Asian country (Khazaria) that converted to Judaism. It later converted to Islam.
The Theory: Modern Ashkenazim are descended from Khazar converts, rather than from the Jews of Judea. The Jews of Judea stuck around Judea and became Palestinians. The Khazar-converts, now the majority of “Jews”, moved to Germany and then decided to go steal the “Jewish homeland” from the “actual ethnic Jews,” the Palestinians.
Thus, (according to the theory,) “Jews” are sneaky thieving conniving evil bastards, (and Palestinians, of course, are totally innocent lambs who would never hurt a fly.)
The reality: Genetic testing is a thing we have, and we can pinpoint pretty darn accurately where someone’s ancestors came from.
Genetically, Ashkenazim are about half Italian and half Middle Eastern, with no admixture from the Khazar region of Asia.
Even if Jews had significant Khazar ancestry, it wouldn’t actually make any difference, but it happens that they don’t. Ashkenazim are less than half the population of Israel and about 75% of the world’s Jews, according to Wikipedia. The most controversial thing you can say about this is that the Italian half is on their mothers’ side, which appears to be true for virtually all diasporic Jewish groups. Men moved to new places and took new wives.
Additionally, we have a fair amount of documentary evidence of where the Ashkenazim came from, since they were often explicitly invited into newly-founded German cities by bishops and princes who thought a Jewish community would make their new cities more economically productive. (Eastern German cities are very recent, on a European scale.)
In short, the theory is just completely false.