Complex sentence: Between 1880 and 1910 up to 30,000 German Jews served in the Prussian Army but none were promoted to officers while, of the 1,500 Jews that converted to Christianity, 300 were promoted.
Split into simpler sentences: Between 1880 and 1910, up to 30,000 German Jews served in the Prussian Army, but none were promoted to the rank of officer. However, among the 1,500 Jews who converted to Christianity, 300 were promoted.