Complex sentence: The Jewish population of Vancouver was still too small to support multiple synagogues; therefore in 1919--1921 the remnants of the Reform congregation joined with the larger Orthodox congregation, Schara Tzedeck, to build a new synagogue in the East End for all Vancouver Jews.
Split into simpler sentences: The Jewish population of Vancouver was still too small to support multiple synagogues. Thus in 1919-1921 the remnants of the Reform congregation joined with the larger Orthodox congregation, Schara Tzedeck, to build a new synagogue in the East End for all Vancouver Jews.