Complex sentence: Many among the Left whose fortunes had declined since the start of the FARC insurgency hoped a peaceful negotiation with FARC, which required a Santos victory, would help rehabilitate the left among the Conservative-Liberal dominated political scene in Colombia.
Split into simpler sentences: Many among the Left that had their fortunes decline since the start of the FARC insurgency and hoped a peaceful negotiation with FARC, which required a Santos victory. This they hoped would rehabilitate the left among the Conservative-Liberal dominated political scene in Colombia.