Complex sentence: Tobiah was an Ammonite official (possibly a governor of Ammon, possibly also of Jewish descent) who incited the Ammonites to hinder Nehemiah's efforts to rebuild Jerusalem.
Split into simpler sentences: Tobiah was an Ammonite official (possibly a governor of Ammon, possibly also of Jewish descent). He incited the Ammonites to hinder Nehemiah's efforts to rebuild Jerusalem.