Well, so much for that treaty. It lasted a solid day or two.
On The Originals Season 1 Episode 18, the peace that Elijah had arranged between humans, vampires, werewolves and witches went out in a blaze of smoke.
Sorry, correction: it went out in a bloodbath, as Marcel compelled some humans to slit their own wrists at a party in honor of the new witches, the vampires there couldn't control themselves and dead bodies were left in a chaotic wake.
No wonder this installment was titled "The Big Uneasy."
In response to Marcel intervening in the city's calm, Elijah killed Thierry. He tore the guy's heart out of his chest right in front of his best friend.