Complex sentence: In World War I he served without distinction as a soldier from 1915 till 1918 and later fought as a member of "Freikorps Rossbach" in Upper Silesia.
Split into simpler sentences: In World War I he served without distinction as a soldier from 1915 to the end of the war in 1918. He later fought as a member of "Freikorps Rossbach" in Upper Silesia.