Which preposition to use with vlachs

in Occurrences 2%

His model is the Rumanian propaganda among the Vlachs in Macedonia, and his expectations are great: "There is no power in Persia to put down such a movement, because it could do no harm to anyone.

of Occurrences 1%

The Romance-speaking Vlachs of Pindus moved down into the Thessalian plains.

Which preposition to use with  vlachs