Complex sentence: By the end of the year, party membership was recorded at 2,000, many of whom Hitler and Röhm had brought into the party personally, or for whom Hitler's oratory had been their reason for joining.
Split into simpler sentences: By the end of the year, party membership was recorded at 2,000. Many of whom Hitler and Röhm had brought into the party personally, or for whom Hitler's oratory had been their reason for joining.