Complex sentence: Before the 1920s, Sannomiya was just a edge of the city, and the major downtowns of the city were Motomachi and Shinkaichi, where are west of Sannomiya.
Split into simpler sentences: Before the 1920s, Sannomiya was just an edge of the city. The major downtowns were Motomachi and Shinkaichi, which are west of Sannomiya.