Complex sentence: The SdP merged with Hitler's NSDAP on 5 November 1938, Henlein himself joined the Nazi Party in January 1939 and was appointed Reichstag deputy.
Split into simpler sentences: The SdP merged with Hitler's NSDAP on 5 November 1938. Henlein joined the Nazi Party in January 1939 and was appointed Reichstag deputy.