(Covers information from Anderson's universe)
The Battle of Las Vegas was a battle between Claire Redfield's convoy and the Super Undead unleashed by the Umbrella Corporation in the ruins of Las Vegas.
Background
In order to create "an engineered apocalypse", Doctor Alexander Isaacs and the Umbrella Corporation unleashed the T-virus upon the world, creating a global pandemic that destroyed most life on Earth. After the Hive outbreak and then again after the Raccoon City Incident, Umbrella experimented upon security operative Alice with the T-virus, resulting in her body bonding with the T-virus and it ultimately giving her incredible abilities, including telekinesis. While Umbrella ultimately let Alice escape as part of "Program: Alice", she learned of their ability to detect her via satellite, particularly when she used her telekinetic abilities and began hiding from them successfully. Unable to reacquire Alice and having realized that her blood held the key to curing the T-virus, Umbrella scientists, led by a clone of Doctor Isaacs, began using a series of Alice clones in their efforts to find a cure instead. Their efforts, while ultimately unsuccessful, led to the creation of the Super Undead using a serum developed from the clones blood.
At the same time, the real Alice encounters Claire Redfield's convoy in the Nevada desert after learning of a safe haven in Alaska called Arcadia. Alice arrives as the convoy suffers a massive attack from a flock of Undead crows, resulting in the death of several members of the convoy. Alice uses her powers to telekinetically redirect a flamethrower and incinerate the crows, but in doing so, draws the attention of the White Queen who is able to use an Umbrella satellite to successfully locate Alice. In order to reach Arcadia, the convoy needs to refuel and Las Vegas is the only place close enough that has the resources they need. Predicting this move, Isaacs fakes a message of permission from Chairman Albert Wesker and moves a cargo container filled with the new Super Undead to the streets of Las Vegas, placing it where it will block the convoy's route and they will be in position for him to ambush the convoy with the Super Undead. Isaacs also sets up a command post on a nearby rooftop so as to use a chip implanted in Alice and an Umbrella satellite to "shut her down" so that Umbrella can capture Alice.
Battle
Finding the container blocking their way to supplies, Claire has the members of her convoy spread out, sending Chase up a replica of the Eiffel Tower with a high-powered assault rifle to provide covering fire if need be. As Mikey gets a winch to move the container out of the way, Alice's suspicions are drawn and she approaches the container. Hearing the Super Undead moving within, Alice realizes its a trap and orders everyone back as the container opens.
The Super Undead rush from the container and attack the convoy members. As they emerge from the container, several are killed immediately by Alice, Claire, Carlos Oliveira, Chase and Mikey, but they start to spread out and several chase K-Mart as she makes a run for a convoy truck for safety. Claire runs after K-Mart to protect her and with the help of covering fire provided by Chase, K-Mart is able to make it to safety inside the truck. Claire and several convoy members come under attack with Chase's covering fire saving a few, but with more being killed by the Super Undead. Though Claire is thrown to the ground by two Super Undead, she is able to kill them before they can harm her. During the gunfight, Carlos loses one of his pistols under a truck and is cornered there by two Super Undead while LJ, running out of ammunition for his pistol, retreats into the truck with K-Mart where a Super Undead attempts to break in and kill them. As the Super Undead gets close to breaking in, K-Mart grabs a shotgun off a mount in the truck and kills it. Carlos is similarly able to reach his pistol and kill the two Super Undead attacking him and a third that catches him by surprise. Several Super Undead attack a truck full of children, but Claire is able to save the children's lives and kill their attackers.
As Alice attempts to save more convoy members from the Super Undead, Doctor Alexander Isaacs watches from his command post and orders an Umbrella technician to "shut her down" and his men to move in fast to get a sample of her blood "while its still warm" for his work on creating a cure to the T-virus. Once all of the Super Undead in Alice's vicinity have been killed, the Umbrella technician sends a signal from an orbiting satellite that results in Alice freezing in place. As Alice begins fighting her conditioning, the battle turns against the convoy without Alice there to help. Several Super Undead attack the news van in which Mikey is taking refuge. Out of ammunition, Mikey flees out the back where Claire kills two Super Undead before having to reload her shotgun. As she reloads, three more Super Undead descend upon Mikey and attack. Claire kills them, but too late to save Mikey's life. Another convoy survivor climbs the Eiffel Tower replica as Chase attempts to cover her, but runs out of ammunition. Chase is able to kill two more Super Undead with a revolver, but two more reach Chase and bite him. Chase eventually throws himself and the two Super Undead off of the Eiffel Tower replica, killing all three. In the truck with K-Mart, LJ, who had been previously bitten, turns into an Undead and menaces K-Mart. Carlos saves K-Mart and kills the Undead LJ, but not before he himself is bitten by LJ.
As the battle rages around her, Alice uses her telekinesis to fry a chip in the orbiting satellite, breaking Umbrella's control over her. Horrified by what's happened since Umbrella took control over her, Alice draws the attention of the last two Super Undead on the battlefield and kills them before turning her attention to Umbrella. As Alice races up the stairs to the roof holding the Umbrella command post, the Umbrella technician is able to get a new satellite feed, showing that Alice is heading straight for them. He desperately attempts to regain control of Alice, but this time, she is able to resist Umbrella's efforts. Entering the tent, Alice kills all of the Umbrella soldiers inside as well as the technician, but Isaacs escapes out the back to his nearby helicopter. As the helicopter takes off, a final Super Undead attacks Isaacs, biting him in the shoulder before the helicopter pilot kills the Super Undead. Alice emerges from the tent in time to open fire on the Umbrella helicopter, but ultimately chooses not to, deciding to use the helicopter as an alternative means for the convoy survivors to reach Alaska.
Aftermath
Following the battle, the survivors are able to use the computers in the Umbrella command post to locate the North American Research Facility. Determining himself to be too far gone to save from his bite, Carlos Oliveira sacrifices himself to enable to convoy survivors to reach the Umbrella helicopter and escape to Alaska though Alice chooses to stay behind.
At the same time, despite injecting himself with massive quantities of the anti-virus, Doctor Isaacs' bite by a Super Undead mutates him into a Tyrant and he slaughters all of the Umbrella personnel in the base. Alice is eventually able to kill Isaacs with help from a clone of herself and gains an army of Alice clones from the facility to use against Umbrella.