This is a re summary of a reply I wrote earlier addressing the general question of what factions and character are retained throughout the Fallout series. Or in a more general sense what is the overarching story going on throughout the Fallout games?
Having playing essentially all of the Fallout games I’ve tried to boil down a general timeline and guide for the Fallout universe of what I think is relevant for a general summary.
The Pre-history of the game starts with the Great War. This was a nuclear exchange between the United States and China that lasted only minutes. (If Fallout 3’s DLC is to be believe the first shot was started by aliens).
Before the Great War there’s an petroleum energy crisis leading to the Fall of the EU (embroiled with wars within the middle east). The US annexes Canada and China invades Alaska. Cultural stasis takes over leading to the general 1950’s atomic feel of Fallout and technology reaches a high point of various Power Armors deployed in the US-China war.
*An odd fact to note is that the US is organized into 13 Commonwealths rather than 50 states. Which is why the Enclave flag has 12 stars and an E making up the last star.
Fallout 1 took place in 2161, 84 Years after the great war.
Fallout 2 took place in 2241
Fallout New Vegas takes place in 2281, 39 years after 2 and 120 years after Fallout 1. Making it roughly around 200 years after the bombs.
This makes it four years after Fallout 3.
(As a bonus Fallout 4 is ten years after 3)
Fallout 1 basically set the stage for the concepts of Vaults, the Brotherhood of Steel (Who are basically technology hoarders) and Supermutants. This is set in southern California and the remnants of LA is the only real source of post-apoc civilization.
Within LA there are many factions at play. One faction that comes into prominence later are the Followers of the Apocalypse. These people are general humanitarians focused on almost missionary like work throughout the LA Boneyards.
The other main faction is the Brotherhood of Steel. They trace their origins to former military personnel who managed to survive the war in a hidden bunker after abandoning the Mariposa military base due to the discovery of the FEV experiments there.
The Brotherhood of Steel generally believes in hoarding pre-war technology and knowledge. Although they do fight raiders and other general menaces they do so out of a common threat rather than general concern for others. For the most part they’re a rather insular organization with a quasi-religion technology bent.
A big part of the Fallout 1 plot is trying to stop “The Master” who is creating Supermutants through giant vats of FEV virus goop. After the Vault Dweller (that’s you) blows up the master’s plans, helps several struggling settlements (including a semi-unimportant town called Shady Sands), and recovers a water chip for Vault 13. You are exiled from your Vault for being too dangerous and go to start your own tribe in Northern California.
Fallout 2 follows a great descendant of the Vault Dweller called the “Chosen One”. His tribe sets him out to find a vault-tec technology called the GECK to help revive their community’s dying agriculture. Along the way the Chosen One runs into a new growing post-apoc California.
The Brotherhood of Steel are still around but take a more cautionary observer role in FO2. For the most part they haven’t changed though and are still xenophobic tech gatherers.
The two important factions to come out of this game are the New California Republic and the Enclave.
The New California Republic grows out of Shady Sands from Fallout 1. They’re a legitimate force for good and organization into a city-state in the post-apoc world. Their money is backed with gold, they have an active police force, and have an active ranger force that mostly battles Slavers. They modeled their politics after the old world democracies and have representative senators with a Presidential role.
The Enclave are based on an oil rig off the West Coast and Camp Navarro. They are literally the old US government in hiding, developing military grade hardware, and preparing for the return of what they consider, “pure” humans. The plot of Fallout 2 basically follows them kidnapping vault people and your tribe, along with lots of genocidal thoughts against “unpure” humans and such.
The game ends with the Chosen One blowing up their Oil Rig/ killing the president and scattering their forces.
Here’s where the canon gets kind of weird until Fallout 3.
Fallout: Tactics says that the Brotherhood of Steel is interested in exploring other parts of the United States and sent an airship over to the Mid-West. The ships gets stranded near Chicago and is forced to become its own splinter faction that is possibly more advanced than the original BOS due to a pre-war semi-sentient computer they discover. (Dubious canonical status, in 3 & NV you can find references to a Chicago based BOS faction but nothing more)
Brotherhood of Steel was a topdown shooter thingy based in Texas and broke all sorts of canon. It’s generally considering to be the black sheep and we don’t talk about it.
Fallout 3 is based on the East Coast DC area is probably what most newer gamers are familiar with. However it’s connection to Fallout 1 & 2 is kind of... odd.
The Enclave is back with the idea being that after their defeat in Fallout 2 the entire organization packed up and left for the East Coast and so happened to resettle into the Capital Wasteland.
The Brotherhood of Steel is back, but this is some kind of expedition fleet that decided to deviate from it’s original mission and become goodie goodies. Those who refused to change the concept from tech gatherers to peacekeepers became the Outcasts.
Supermutants are back. This has to do with one vault full of FEV virus vats that give a different effect to these east coast super mutants. So they’re significantly dumber, with different skin color, and have different sizes.
It should be noted that there is a small side quest involving an android known as a synth hiding from “The Institute”; an organization based in Boston. This becomes the center story of Fallout 4.
The storyline of 3 in short summary is that the Enclave is destroyed for good this time and the Brotherhood of Steel distribute free water throughout the Capital Wasteland.
Fallout New Vegas the story returns to the west, specifically the Mojave Wasteland.
The New California Republic has grown massively since we last saw it 39 years ago in FO2.
They’ve more or less taken over all of California and integrated or defeated their factional rivals (Vault City). The original Brotherhood of Steel engaged in a war with the NCR since they were afraid of their status being challenged. They lost and the NCR broke the Brotherhood of Steel leaving many of the West Coast chapters to go into hiding.
The NCR itself is now embroiled in a two front expansionist campaign in Baja California and the Mojave Desert.
The goal in the Mojave is to control Hoover Dam because the NCR is running into a problem of too much too fast. While things are generally peaceful in California their resources are now being spread thin and this is driving them to push into new areas to try and keep their population supplied. With a much larger government general incompetence has set in as well. While the NCR is still well meaning they are a shadow of the morals they started off with, more concerned with bureaucracy and territory than the good of the people.
However in the East a former band of Followers of the Apocalypse (a humanitarian group that started in Los Angeles) started a group of tribals that kept absorbing more and more tribes into it forcefully. Until it numbers around 87 tribes and became a massive army under a new leader renamed Caesar.
Using pre-war knowledge Caesar has organized this group based on the Roman Empire of old and has named it Caesar’s Legion. To the tribals that run the Legion, the concept seems like divine inspiration of the Gods through Caesar with little knowledge of its pre-war basis. Life in legion territory is brutal but efficient. So brutal that there are in fact no more raiders in their territory so trade is more or less completely safe. However nobody gets any rights at all if you’re not a slave or a legionnaire.
Believe it or not the west coast Enclave is still around too but now they’re all old retirees just trying to stay under the radar of the NCR. You can meet some of them in New Vegas though.
The Supermutants from Fallout 1 are also still around and they’ve mostly moved on to create their own little societies. Some of them violent and others not so much.
This brings us to Fallout 4 which is much more in the line of Fallout 3. Where this time the goodie East Coast Brotherhood of Steel has been taken over by a new Elder (who just so happens to be a kid transplanted from the west coast in Fallout 3 and related to the original founder of the BOS).
The Brotherhood of Steel in the Commonwealth has returned to being xenophobic technophiles but have now added synth genocide to their to do list.
The Institute now plays a central role in Fallout 4, expanding from their brief mention in Fallout 3.
They have used their advanced technology to infiltrate the Commonwealth with Synths.
There are some slight mentions of the NCR and the west in general in Fallout 4, but not a huge amount.
Some speculate that the NCR might have won in New Vegas since they’re mentioned at all rather than Caesar’s Legion.
And that’s the history of the common connective threads between the Fallout games in a nutshell.