On Natural Instincts, the story of The Originals starts right at the beginning of season 1, but with Marcel and his crew coming to the Originals instead of The Originals coming to him (and some other slight changes)
History of Crescent and NEA Packs
They were all united as the Crescent pack, originating from New Orleans. After an internal war, they split up, and part of the pack moved to a village in what is now Virginia. They became the North East Atlantic Pack (NEA Pack). At around 1000, Esther got involved with with the NEA pack leader Ansel and had Klaus -starting the chain reaction that creates the first daeva vampire family.
Vampire Sheriff of New Orleans
Marcel had become vampire sheriff of New Orleans - unofficially, after the Mikaelsons fled the city thanks to Mikael. He worked hard to rebuild at least the simulation of peace and order. He quickly rose in rank with the vampires there, earning their respect and loyalty.
In the 1990s, the Crescent wolves and the vampires got into a war. Marcel exerted his authority, and ended this war by getting a witch to place a curse on the pack. Since then, the wolves would be in their animal forms every day except on full moons, when they turned human again. A good handful of wolves escaped this fate and fled New Orleans - eventually ending up in NYC.
Around 2005, when Hurricane Katrina hit, all eyes were on the city - and Marcel, loyal to his people and the city, did not run off like some other older vampires would. He stuck around and helped vampires and humans alike, and played an active part in trying to rebuild the city. This caught the attention of the Authority, who had been secretly trying to ramp up the power of the vampire monarchy. They understood other species of vampires were out there, but wanted to keep everything secret to maintain control. Having seen Marcel's role in New Orleans, they approached him - explained their cause, and officially named him sheriff of New Orleans. From there, he had met with other sheriffs like Eric Northman of Bon Temps, Louisiana.
For the ones who did follow him, it was a party every night. But he ruled his area with an iron fist, having a lock down on the werewolves.
For the witches - this happened by chance. In 2013, Marcel had been notified of the Harvest witch ritual and went to stop it, seeing that the girls were being slaughtered. He came just in time to save Davina and take her away. Since then he's kept her secluded and safe, away from the other witches. From there she was able to tell who was using magic in the city. This allowed Marcel to ban the use of magic in New Orleans.
And for the vampires, he developed a large and tight nit community. Those inside his 'inner circle' were granted daylight rings. Those outside of his circle were called 'night walkers.' After the Great Revelation in 2010, with all of the anti-vampire sentiments growing across the nation (and starting to spill into New Orleans), a part of Marcel wasn't surprised when he got a message from The Authority, asking him to serve as sheriff in New York City (replacing Killian Brandt, who mysteriously disappeared) - the epicenter of supernatural activity. Marcel was inclined to ignore it - which was a risky move considering no one really says no to the Authority. But Marcel loved New Orleans too much, and was planning to see how long he could ride this out without responding to their request.
Meanwhile, Celeste - a former lover of Elijah's who had been 'killed' thanks to Klaus - had long been possessing Sabine's body. And for a while, she stayed under the radar of Marcel's rule without much issue or fanfare - befriending the coven of witches like she always did over the years. However this time, training them in in magic was not easy - if not virtually impossible. She was going to use the power of the harvest but she recognized she might need more power than that to accomplish what she wanted to do. She became impatient. So she started to set up sacrifices around the town to perform expression - it started with the hex placed on the priest that killed an entire church of people. The next would be what changed everything. She lifted the curse on the Crescent werewolves. Not only that, but she granted them the ability to change whenever they wanted, temporarily.
This is something that Davina felt, but by the time Marcel could do anything about it, it was too late. A family of vengeful werewolves were after him and his crew. And it was exactly as Celeste planned, hoping the fall of Marcel's empire (and ideally, the death of Marcel himself) would draw out Klaus and the Originals.
A Werewolf ProblemThe werewolves attacked mercilessly, biting and killing many of Marcel's people - completing the second sacrifice that Celeste needed. Marcel refused to back down of course, as stubborn as he was. But his right-hand man Thierry was at his ropes end when his girlfriend Katie perished in the middle of the vampire/werewolf war.
Thierry shouted out in a pained cry as he punched a wall on the balcony of the compound. Brick debris crumbled to the ground, and he sobbed silently.
"Thierry..." Marcel started.
"I loved her, Marcel," Thierry said, looking over his shoulder at him. "I loved her - and they killed her."
"I'm sorry," Marcel told him, sincerely. "T, I promise you, we will make them pay for this. You just got hang in there with me."
Thierry quickly turned around. "For how long?" he snapped. "I don't know how they did it or where they got it from but these wolves are powerful, more powerful than us."
Marcel shook his head, knowing what he was about to say. "I'm not running, T. This is my home, this is my city, and I'll be damned if I'm going to let some werewolves run us out."
"At what cost, Marcel? Until we're all dead? Because then you won't have a city to rule anymore if you're lucky to survive this."
There was a brief pause, Marcel wanting to say something but couldn't. Thierry sighed. "We can't go on like this, Marcel. I know you don't want to run, but we're out of options. I think it's really time to consider that deal with the Authority."
Marcel refused, he wasn't going to let what he had built go down without a fight - New Orleans was his home. But of course that was the problem, they had been fighting and they were losing. Still undecided, he went to Davina and told her the situation. Davina said that she trusted Marcel and even admitted she wouldn't mind a change of scenery, so long as the other witches don't find her. Moving out seemed like the best option for both of them. So finally, but reluctantly, Marcel made the move - taking what was left of his crew (those who wanted to follow) with him.
Hybrid Origins & Family Reunions
A little while after The Great Revelation - Klaus had succeed in becoming a hybrid and had "convinced" Stefan to become a ripper in exchange for Damon's life (who was going to be used in the sacrifice). He thought he'd make things interesting by undaggering Rebekah - Stefan's former lover. All three travelled together - trying to make hybrids with no success...until they realized they needed Elena's blood to complete the process. They made the trip back to NYC and succeeded in obtaining enough of Elena's blood to create a hybrid army.
The first person he turned was Tyler Lockwood. He also turned a woman named Hayley Marshall, who had been traveling around on the search for her family. At the time, she'd been carrying out a deal with Atticus Shane. Shane promised her that he would help her find her family if she carried out some tasks for him which would release Silas from his tomb. Those tasks involved setting the stage for mass sacrifices to generate mystical power. When Hayley turned into a hybrid, Shane taught her how to beat the sire bond, then asked her to get as many hybrids unsired as possible. Hayley did this with the help of Tyler.
Eventually, however, Klaus discovered that several of them had betrayed him - and so he slaughtered a good majority of the army, save for the unsired hybrids who stayed out of the crossfire. Tyler has built a small army of his own, and they were fired up because of the senseless slaughter of their families and friends. So Tyler was appointed pack leader and Klaus' attention was completely on him while Hayley slipped off to continue her quest.
Sometime after Stefan, Rebekah and Klaus returned to NYC - Stefan was plotting revenge for everything Klaus had done. So he released Klaus' entire family, including Esther (with the help of Bonnie).
Crescent and Wolf Packs
Hayley had came to New York, thinking Shane had a lead on her family. After the hybrid mission was out of her hands, she was about to leave, but then she discovered a roaming wolf pack in a trailer park (a rare sighting in the city) by the docks. Someone recognized her birthmark and claimed that it was that of the Crescent clan. Jackson Kenner, a leader of the pack, told her everything. How they fled New Orleans from Marcel, how they were betrothed to each other, and more. Hayley, of course, was certainly not ready to make commitments. So she spent some time alone, first going to Marcel - in a rage, at first, for his crimes against her family. But then Marcel told her how he saved her as a baby, tried to give her a life outside of the fate of the rest of the wolves. In exchange for this information, Hayley promised to do what she could to keep the Crescents at bay.