Petras Moravian Birth Place

Vaclav/Wenzl/Wenceslaus/James Petras & family arrived in Baltimore aboard the Steamship Baltimore on 4 Sept. 1871. Departed from Bremen, Germany. He and family members were born in Moravia. Destination was Cleveland. Majority of the family moved to Tabor, SD in 1879, then some to Tony, WI in 1899.

Does anyone know how to trace back from Bremen to their home town in Moravia?