Actually I heard from a Choshuv Rav that Sefardim are from Yehuda and A are from Epharim
The Chida says that Sephardim are from Yehuda, And Ashkanazim are from Binyamin. Hashem put Binyamins children in Europe because their ancestor never bowed in from of Esav (parashat Vayishlah). People of Binyamin are tougher people. They could withstand bnai Esav.