Las Vegas is home to the largest Luxury Arcology on Earth, the The Jewel of the Mojave.
Outside the Arcology walls, American Motorized Combat League (AMCL) serves as a combination of military, mercenary army, raider group and combat sporting league. It successfully defended Las Vegas' borders from the incursions of La Sindicato ("La Sín") during the Second Mexican-American War ("La Reconquista"), at which point occurred the LasVegasSecession.
The territory is officially claimed by United Mexican States, but neither side wants to engage in a costly and destructive war, so they are for now content to let the dispute rest.