Fallout: New Vegas Factions

Major Factions
The following factions, with the addition of Mr. House, are the 3 major players in New Vegas. During the course of the game, you will eventually have the option to side with one of them, or go it alone, to the expense of your relations with the other major factions.
 * Caesar's Legion
 * New California Republic

Minor Factions
The following factions can be recruited as allies (of you and the major faction you ally with, if any) in the climactic battle.
 * Boomers
 * Brotherhood of Steel
 * Followers of the Apocalypse
 * Great Khans

Petty Factions
In addition to the Brotherhood of Steel and the Great Khans, the following are parties you can choose to destroy or spare if you choose to go it alone instead of siding with one of the 3 major factions. All three of these factions run casinos on The Strip.
 * Chairmen
 * Omerta
 * White Glove Society

Other Factions

 * Crimson Caravan
 * Fiends
 * Gun Runners
 * Jackals
 * Bright Brotherhood
 * Kings
 * New California Rangers
 * Powder Gangers
 * State of Utolbitha
 * Nightkin
 * Vipers
 * Van Graffs