The Four Horsemen of the Apocalypse are seen as the beings that herald the end of the world, casting their shadows across the realm of humanity and bringing about the day of judgement. There is no negotiation when the four brothers appear because this why they exist, to maintain a balance until such a time as they are called. They hold no allegiance to the denizens of Heaven, Hell, or Earth and help to decide the fate of all three at the end.
They’re governed by their own rules which have been written up by the Charred Council. They can’t act without the seven seals being broken, but sometimes things go wrong and action must be taken. In Darksiders, Heaven and Hell bring their battle to the Kingdom of Man, which is a sign of the Apocalypse, and the horseman War arrives on the scene to begin the operation he has been created to do. It’s quite soon after though that he realises that none of his brothers turned up and he has been tricked.
This is where you have to look at those who brought the war to Earth, Abaddon, the leader of Heaven’s Hellguard and the demons of Hell. Abbadon is one part of the pair that decided to bring about the Apocalypse earlier than intended, at a time before the human realm was strong enough to join the battle. It isn’t due to any malice against the realm of humanity but instead a tactical choice of a general who sees that Hell’s army is gaining the upper hand and that he needs to take the fight to them immediately.
Of course the presence of War disrupts the plan and Abbadon is defeated on the battlefield, with his own soul transported to Hell where he accepts a new power and becomes the Destroyer. In this new form, Abbadon guards the final seal, but he also now has a grudge against Heaven who didn’t come to help him, and so plans to lead an assault against that kingdom. It’s not a choice that can be regarded as being without merit. After all, he was left for dead and he sees that as a betrayal.
The other half of the pair is Azrael, the angel of death, who shared Abbadon’s fear of a powerful Hell army. However as Azrael sees the plan fail he decides to switch sides and help War regain his power so that he has a fighting chance against the forces that conspire against him. Azrael reveals what happened and with the help of the Tree Of Knowledge also shows that The Charred Council knew about all of the plans the entire time.
The Charred Council knew of the early Apocalypse and let it happen for a number of reasons. First it wipes away one Kingdom instantly, making it a lot easier to maintain a balance. Now it’s just Heaven and Hell who are equal in strength, without the much weaker human kingdom putting the balance in a precarious position. Of course, the Council can’t interfere in the actions of Heaven and Hell directly, so summon War themselves to get rid of Abbadon and Azrael.
The Council is keeping its own mission in mind when doing this as the two angels threaten the entire power balance that exists, and killing them off helps to settle it. This all backfires as War refuses to kill Azrael, meaning the Council need to bring War down as he becomes a threat to the balance between the realms too. As the Council loses control of War, they must surely realise that he will now seek his revenge against them, and they’ll have to do whatever they can to stop him.