Wars in general are fought by greed. The civil war was no different.. The south had every legal right to leave the union.. So Lincoln did what he could to antagonize the south into reacting aggressively.. To give you an idea after Davis was captured and "arrested" he was held in prison for many years.. The north could not bring charges against him since he was duly elected by the confederate states.. He eventually was released after the united states tried to weigh the options of charging with treason amongst numerous other charges.. But none would stick..
But yes, history and the victors are allowed to write the history books.. And putting a moral and ethical spin on war is paramount to justify their greed.