When borders changed sometimes ethnicities changed with them. For instance
I was told that Rav Meir Arak and so naturally my mother's mother's sister
Hinda (Renke) Arak were Eastern Galitzianers (Ukrainian Galitzianers)
I amusingly can claim myself then in a larger sense as partially Romanian
since I learned that it is true but only because borders switched and in
this case so did ethnic identities but in some instances like in the
Lublin area peoples ethnic identities stuck with Polish. People move and
ethnic identities don't always switch.
Yisrael Asper
Pittsburgh PA