Vampires: The Turning

For many centuries, the phi song neng (vampires who have vowed never to drink human blood) have lived among the villages of the Far East. One day over 800 years ago, a young human warlord named Niran fell in love with one of the song neng, a woman named Sang. Niran wanted Sang for his own, so he killed her husband and son. In her pain and rage, Sang attacked and bit Niran during a Songkran (New Year) solar eclipse, turning him into a vampire. From Niran's bloodline have come many jai tham (vampires who drink human blood and kill for pleasure). Only Sang can end the jai tham's nightly attacks on humans. Doing so, however, will end the entire bloodline and turn every vampire, song neng as well as jai tham, into mere mortals again. Since the coming Songkran festival will feature the first solar eclipse in 800 years, Sang intends to kill herself by exposing herself to the sun's rays at the end of the eclipse and thus wipe out all the vampires in Thailand.
Connor (Colin Egglesfield) and Amanda (Meredith Monroe) are vacationing in Thailand during this year's Songkran festival. Connor, trained since childhood in Muay Thai (Thai boxing), takes Amanda to see a match. However, Amanda cannot take the brutality and goes back to their hotel alone. On the way, she gets lost in the Phang Nga market, and Mr Nice Guy (Dom Hetrakul) offers to show her the way to her hotel. He leads her on a short cut down a deserted alley, then turns into the vampire Niran, drinking her blood and carrying her off on a motorcycle. Connor tries to follow, but he is stopped by another vampire, obviously intent on killing him. Just as the vampire is about to succeed, a bald-headed man appears and chops off the vampire's head. Connor begs for his help finding Amanda, but he warns Connor to leave Thailand immediately and threatens to kill Connor if he follows him. Connor stealthily follows Kiko (Roger Yuan) home to Kong Sai House.
When the police refuse to consider Amanda missing until 48 hours have passed, Connor goes back to Kong Sai House, only to find everyone asleep. While snooping through the house, Connor is attacked by Sang (Stephanie Chao). Connor gets away from her by jumping out a window. As Connor lands on the ground below, he is stopped by vampire slayer Raines (Patrick Bauchau) who insists on testing Connor's blood to see if he is infected. When Connor comes up clean, he begs Raines to help him find Amanda but, like Kiko, Raines warns him to leave Thailand. Amanda is as good as dead, Raines says. If she resists, the jai tham will bleed her dry; if not, they'll turn her, and then Raines will slay her (he gets $10,000 for every vampire he kills). Either way, Amanda should be considered dead to Connor.
Connor won't accept it and returns again to Kong Sai House. While there, he sees a photo of Niran in front of the Techno Games Arcade near the Phang Nga market. Figuring that Niran might have taken Amanda there, he snoops around. He finds Amanda being held in a cell with skeletons, carcasses, and other humans in various stages of having their blood drained. Amanda and Connor escape but are attacked outside by two jai tham on a motorcycle. One drives off with Amanda; the other stays to kill Connor. Just as Niran and the rest of the jai tham arrive, Sang appears. Connor grabs a motorcycle and, with Sang riding behind him, they succeed in outrunning the jai tham.
Both Amanda and Connor are now faced with decisions. Amanda must decide whether to allow Niran to turn her or to keep on drinking from her, which causes acute pain. Connor has to decide whether or not to join the song neng in hopes of winning the battle with the jai tham and helping Sang to kill herself so that all vampires (including him) will be turned back into mortals. The alternative, if Sang is not successful, is that Connor will remain a vampire until the next Songkran eclipse rolls around in 800 years and Sang can try again. Connor's decision is made doubly hard because he is attracted to Sang. Amanda decides to continue resisting, and Connor decides to become song neng. This requires being bitten by Sang.
The day of the eclipse is upon them. The song neng have made a deal with the slayers. Since Sang's embrace of the sun must take place in the same spot where the curse began 800 years ago (a couple blocks away), the song neng have made a deal with Raines. Raines and his slayers will line the buildings and walls that overlook the site, which looks like an archeological dig, in order to kill any jai tham who try to stop Sang. Connor, Kiko, and the rest of the song neng will help Sang get to the required spot. The eclipse starts at 3:00, and they will have 17 minutes to do the job. All is set.
The jai tham arrive on their motorcycles. In the melee that follows, Connor and Niran fall through a weak spot into a pit where they continue fighting. Time is running out, and Kiko realizes that the slayers have double-crossed them. The slayers open fire, shooting everyone, song neng and jai tham. Only Connor and Niran remain protected in their hole. Connor manages to impale Niran, but when he surfaces from the pit, Connor finds only bodies. He shouts for Sang, but there is no answer. Raines walks up, gloating over how much he will get for all the vampire heads AND those in the future. If Sang ends the curse, he explains, there's no more vampires, and we're in the vampire hunting business.
Connor locates Sang as Raines turns his crossbow on her. Connor offers to shoot Sang so that she does not have to suffer. Raines hands his bow to Connor. Connor aims at Sang but suddenly swings his aim to Raines. Forcing Raines to carry Sang to the designated spot, Connor gives her one last kiss before the sun reappears. She explodes, taking Raines with her. Connor hurries back to the jai tham's base and rescues Amanda.

Question: What began 800 years ago?
Answer: A curse.