The Cataclysm

Preparations
The Cataclysm was Ra's al Ghul's plot to purify Gotham City and take revenge on Bruce Wayne for running away from the League of Assassins and his daughter Talia. Phase 1 of the plan was to destroy Gotham City, phase 2 was to torture and replace Batman. The first attempt was unsuccesful, because Joker killed Jason Todd.

In order to achieve this, Ra's decided to create four Horsemen of the Apocalypse, a group of experimental warriors overseen by El Pentiente, replacing a project that Ra's al Ghul was not satisfied with. Together, this quartet were meant to oversee Gotham's cleansing and the removal of the Batman:

Lilith (Larissa Diaz) - The scout of the group, Larissa Diaz was named Lilith and would stalk the city until she located Batman and use her talents to poison the Batman, little by little, to keep his mind clouded and prevent him from performing at his peak performance, ensuring chaos would reign in the aftermath of the League's engineered earthquake.

Abaddon (Bane) - The muscle of the group, a prisoner from Santa Prisca was named Abaddon and was surgically grafted to an injection system which would fuel his muscles with an enhanced steroid concocted from the chemicals of the Lazarus Pits. With a mind able to match the Dark Knight in tactical analysis and a body surpassing the abilities of the Batman, Abaddon was trusted with defeating and capturing the Batman.

Dumah (Jason Todd) - Ra's usurped the body of Jason Todd, a young man killed by the Joker, who had been trained by Wayne and using the Lazarus Pit, arcane rituals, forbidden science, and torture, Ra's reshaped the young man into an assassin worthy of helping to bring down the Batman. It was left to him to assist the other Horsemen in logistics and tactics, providing them with the vital intel they would need to overcome Gotham's caped crusader. Once the Batman was captured, Dumah would oversee the torture and torment of the captive Bruce Wayne, making certain that he was at his lowest before he would be released from this world.

Azrael (Jean-Paul Valley) - Given the honor of executing the Batman was Azrael, an experiment from birth overseen by the League and crafted into the ideal assassin. Once the Batman was removed from this mortal plane, Azrael would then become Gotham's new champion, helping the League to usher in a new age for the city, guided to new heights by Ra's al Ghul...

The Undertaking
The Undertaking was a trial run of the Cataclysm, a test of the artificial Earthquake machine and a small jailbreak of prisoners in Star City and then a systematic attack on Oliver Queen by the League of Assassins. It was called off so as to not risk tipping their hand that their true target in doing was ultimately Gotham. There were no Horsemen, but the League tried attacking his character and him in person repeatedly, trying to wear him down. They actually beat him unconscious in his own home and set fire to his family home, but John Diggle saved his life. Another common thing they would do is call him and make him aware of two imminent attacks against his loved ones and then see which one he'd go to protect. Sometimes they'd carry out the attacks and if Olliver didn't show, leave their target battered and broken, or they'd just video tape him going to save the other person and mail it to the target that Olliver chose not to save. Sometimes, they'd do both.

No Man's Land
On the anniversary of the death of Jason Todd, November 1, 2007, in Gotham, the League of Assassins set off an artificial earthquake in Gotham, timed with explosives on the city’s bridges, and a coordinated unleashing of powerful weaponry to the city’s criminals and a mass escape at both Blackgate Prison and Arkham Asylum. This day and the time that followed as since been coined "The Cataclysm of Gotham".

With Gotham declared a No Man’s Land by the US government, Batman was left to restore order in Gotham and capture every single escapee. Easier said than done, that was a task made more difficult by the Four Horsemen. While Lilith carried out her assignment, the second Horseman, the assassin now known as Bane, got carried away. November 22, 2007 he captured detectives Bullock and Bard and Captain Gordon and challenged Batman at the top of GCPD. After beating the Dark Knight to within an inch of his life, he strayed from the plan and tried to kill the Batman by throwing him over the side of the GCPD Headquarters. Batman was able to grapnel to safety where he was picked up by his new apprentice Tim Drake and his faithful friend Alfred Pennyworth who managed to get him to safety.

With the League’s plan in flux, Dumah began to regain his memories. El Penitente’s brainwashing was shown to be faulty when the League attempted to use Vanguard as a horsemen, but it all came crashing down on Jason. He took over the biker gang known as the Order, changed his name from “Dumah” to “Saint Dumas”, and started taking over the criminal underworld. As Saint Dumas did so, Azrael watched from the shadows, hoping that Dumas would lure Batman out of hiding.

The League also hadn’t counted on one of it’s most skilled trainees arriving in Gotham to fight off the criminal scum that was seizing it. Oracle, Black Canary, and Huntress rose up to fight back as Dick trained Tim in the Batcave. They came across this trainee, who was operating as The Nothing, and determined to give this city hope once more, they gave Cassandra Cain a suit as she became the third Batgirl. While Bruce was recovering, his first protégé, Dick Grayson was called in by Tim to become the new Batman and help restore order in Gotham. As Tim officially debuted as the third Robin, they began taking back their city with help from others such as the Birds and Bruce’s cousin, Kate Kane, the vigilante known as Batwoman. Black Lightning also steeped up to protect the Bowery and East End from chaos.

As Dumah’s black mask began to rust, he came into conflict with the new Batman and Robin. As the three brothers battled it, Dumah’s red mask was knocked off. Seeing Dick caused his memories to rush back to him, and used his brother’s confusion to escape. Azreal looked on as Batman defeated Dumas, turned the Order against their master, and discovered the identity of the masked Horseman as one of his fallen comrades. As Batman pursued a fleeing Dumas, Azreal made his move and confronted the exhausted Batman.

Though thrown-off by this Batman’s techniques differing from those he had trained to counteract, Azrael did manage to defeat Batman by making use of a bullet wound inflicted by Dumas. However, his programming went haywire as he was meant to kill Bruce Wayne’s Batman, not Dick Grayson. He knew he would never be Gotham’s champion like the Batman had and simply walked away, leaving an unconscious Dick Grayson to discover Azrael’s mercy when he regained consciousness. He took over the Order and became dedicated to the Batman instead, renaming the biker gang "The Sons of Batman".

Bruce became more dedicated to recovering, returning to a better state with a drive to find Jason. With his city finally back under control, Bruce finished his long road to recovery and returned to the cape and cowl.

Aftermath
In the Aftermath of the Cataclysm Amanda Waller saw an opportunity to establish an international agency dedicated to pursuing global threats and investigating the rise of meta-crime. The result was ARGUS, a United Nations’ sanctioned intelligence operation overseen by Maxwell Lord, with Amanda Waller herself as the deputy director. Under the umbrella of ARGUS, the JLA founders and original members were invited back to found a new team, an international team simply known as the Justice League.