In an apocalyptic world such as Fallout, raider gangs and similar factions are pretty much inevitable, so let's see some ideas you have for raider gangs/factions. Some that aren't simply just called "Raiders" like in FO3/4. The Edmonton Rebels On the day of the Great War, a small cell of liberation fighters from Alberta fighting against the US annexation of Canada ambushes and seizes a Vault in Northern Montana, killing the Vault Dwellers who were meant to shelter there, and sealing themselves off while the world they know burns around them. Unbeknownst to them, the Vault's purpose was to be the last old world dairy and livestock farm, and as such the Vault was only given enough food for a couple years as the Dwellers, who were farmers hand-picked to reside there, were meant to live off the cattle. None of the Rebels were capable farmers, and the cattle eventually died out due to mistreatment, sickness, or being eaten, leaving them with nothing after their food/water was spent. With no resources left, they turned to the outside world, desperately sacking what little settlements or scavers they come across in the early years after the war, usually raiding in the nighttime as to not give away their Vault base of operations.