Complex sentence: O'Banion at first tried to get Torrio to reign in the Gennas, when Torrio did not oblige, O'Banion started hijacking the Genna's shipments.
Split into simpler sentences: O'Banion at first tried to get Torrio to reign in the Gennas. When Torrio failed to do this, O'Banion started hijacking the Genna's shipments.