Complex sentence: After graduating with a law degree, he joined the Nazi Party in 1931, followed by joining the SS. In 1942, he was promoted to the rank of SS-Hauptsturmführer (captain).
Split into simpler sentences: After graduating with a law degree, he joined the Nazi Party in 1931. Thereafter, he joined the SS. In 1942, he was promoted to the rank of SS- "Hauptsturmführer" (captain).