When I was thinking about doing a crossover two games came to mind Fallout and Mass Effect. So I read a few F/ME Crossovers and found out it kind of mixes well. Anyway I figured I would give it a shot.
Disclaimer: I do not own Fallout or Mass Effect.
Updated 11/26/2015: Timeline is updated to include Fallout 4. WARNING: Spoilers.
2077- World War III ends with bombs dropping on China, US, Europe, Saudi Arabia, India, and Russia. Massive amounts of Nuclear Fallout decimates the rest of Earth's Population in regions like Africa and South America and Australia, and parts of the Middle East, but survivors have been reported by scouting expeditions to those regions. Vaults spread thought out the United States and Russia hold the last vestiges of hope for Humanity.
2161- The Vault Dweller is sent out into the wastes to find a replacement of the Vault 13 water chip.
2189- The New California Republic is voted into existence as a sprawling federation of five states: Shady Sands, Los Angeles, Maxson, Hub and Dayglow. The Followers of the Apocalypse rise to become a major influence in New California. Thanks to the Vault Dweller's help, they gain control of the L.A. Boneyard.
2227- The Sole Survivor wakes from his pod only to have his son, Shaun, ripped from his arms and is shot in the chest before he and his wife are frozen, once more.
2242- The Chosen One enters the Enclave's oil rig using the damaged tanker and destroys the Poseidon oil platform, killing the President of the United States and ending the Enclave's plans for world domination.
2247- Graham, Calhoun and Sallow are captured by the Blackfoot tribe for ransom. The young Sallow uses his knowledge to train the tribals in the art of warfare, impressing them enough to become their leader. Sallow assumes the name of ancient Roman emperor Caesar and makes Joshua Graham his right-hand man. He decides to create an empire modeled after the historical Roman Empire, intending to erase the tribals' individual identities and replace them all with a single, monolithic culture - the Legion. He tells Calhoun to go back to the Followers and spread the news of these happenings.
2254- A Brotherhood of Steel squad led by Owyn Lyons is sent to Washington, D.C. on the East Coast to search for technology
2277- Lone Wanderer is forced to leave Vault 101. A series of events in which The Lone Wanderer's father sacrifices himself to help his son get away from the Enclave takeover of the Project Purity and Lone Wanderer joins the Brotherhood of Steel. Lone Wanderer ventures to Vault 87 to find the GECK and is captured by the Enclave. Lone Wanderer escapes destroying Raven Rock in the process. The Assault on Project Purity begins in order to wrest back control of the Enclave.
Meanwhile the NCR and Legion clash at First Battle of Hoover Dam.
2278- Lone Wanderer and Brotherhood assault Adams Air Force Base, and manage to destroy the Enclave's last base of operations in the Capital Wasteland.
2280- Elder Owen Lyons passes away and his daughter Sarah takes his place with encouragement from her husband the Lone Wander as the Head Elder of the Brotherhood Alliance.
2281- Courier is shot in the head in Goodsprings and is revived by Doc Mitchel. Courier proceeds to hunt down Benny of the Chairmen. Upon hearing his reasons for stealing the chip,the courier agrees to partner with him. Courier gets involved in Mohave conflict. The Courier kills Mr. House. The Courier supports New Vegas at the 2nd Battle of Hoover Dam or later, The Battle of the Three Armies. Surviving Intelligent Deathclaws are found by the Courier at Dead Wind Cavern and are welcomed into New Vegas setting up a Community in Vault 3 after the fiends are killed. The Courier sends a couple of Securitrons to protect the Deathclaws from any bigot who might try and kill them.
2283-The Lone Wanderer and Elder Sarah Lyons disappear while tracking rumors of General Autumn's Enclave Remnants in the Northwest Territories and are presumed dead. Their adopted son Arthur Maxson ascends to the rank of Elder bringing back many of the traditional Brotherhood ways while still allowing new human members.
2285-The Brotherhood starts the construction of the massive airship, dubbed the Prydwen.
2287-The Brotherhood mobilizes to the Commonwealth to deal with the Institute leaving a small contingent at the Citidel. The Sole Survivor wakes from Vault 111, and seeing his Wife's pod is too damaged to open safely heads out in search of his son. He makes contact with the Brotherhood via Paladin Danse and forms an Alliance to get his son back whom of which he believes is a ten year old.
He is sent to the Institute were he meets his son, a Sixty year old man and the Director of the Institute. The Sole Survivor leaves after refusing to help the the Institute and their Isolationist and selfish ways. He joins the brotherhood fully despite knowing they were no better and out of revenge. He is tasked with hunting down Paladin Danse who was revealed to be Synth, but refuses to kill his friend, standing up to Maxson in what was known as the start of a more opened minded Eastern Brotherhood. Liberty Prime is activated and the Institute is Destroyed in what is known as the Battle of Cambridge.
Virgil and any hopes of a Super Mutant Cure are lost when he is shredded to death by an feral Alpha Deathclaw laying in wait outside his cave as he tried to leave the Glowing sea.
2288-Eastern Brotherhood of Steel contacts the Midwestern BOS and Texas BOS whom were banished from the Brotherhood for allowing mutants and ghouls into their ranks. The Brotherhood Civil War starts as the Eastern Brotherhood invades Chicago. The Midwestern Brotherhood hosted a massive army as they had a more open policy longer than the Eastern Brotherhood. The war reaches stalemate with the Prydwen Accord being signed allowing Non-standard Humans to join.
2290-The Brotherhood Alliance is formed. The new doctrine for the Alliance allows the conscription of Meta-Humans, Necro-humans and locals. The local populations rally around the Brotherhood Alliance with the Citadel as the Capital. The Brotherhood Alliance focuses on security and shutting down slavers and raider warlords for time being.
After hearing reports of the Brotherhood Alliance, the weakened NCR tries to contact and negotiate peace after hearing about the new reforms the Brotherhood underwent hoping to give itself time to rebuild it forces should the Brotherhood attack.
The Mojave Brotherhood manages to contact the Brotherhood of Steel in Baltimore for support. An emissary is sent. Negations begin, The Mojave Brotherhood reluctantly agrees to reform under the Brotherhood Alliance's doctrine including the conscription of local humans, necro-humans, and meta-humans, and as per agreement places Veronica as the new Elder. An agreement with New Vegas is also created leaving the city-state as a sovereign ally.
2291- Tensions between NCR and Brotherhood Alliance increase after the Brotherhood Alliance demands to NCR to cease all aggression against their Brothers and Sisters in Lost Hills. This leaves the NCR with no room to expand and Surrounded on two sides. The NCR and Brotherhood meet in New Jerusalem for peace talks. It all goes south when the NCR Ambassador is shot by the Courier sparking the 2nd NCR-Brotherhood war. When asked why she did it she said, "The NCR was waiting for an excuse to go war and make it look like they were in the right at the same time. I gave them one." Many have deduced the Courier wished the two powers to clash using her status as a Bortherhood ally to draw the Brotherhood into the NCR crsshairs. Both were weakened by war as Vegas was hardly touched during the fighting.
2294- The Battle of Lake Tahoe takes place. The battles takes many lives on both sides including the Sole Survivor's. A squad of Ten NCR Veteran Rangers were sent to eliminate him. The fight took place in a small ravine near Reno where they had separated him from his squad. Only one ranger made it out alive, but died of her wounds after reporting in. The Brotherhood later discovered that he rigged his medic pump to inject him with Med-X upon running out of stimpacks before his death. His death had the opposite effect the NCR had intended. The demoralizing effect they had expected was replaced by Brotherhood soldiers using his name as a rallying cry at every major engagement from then on.
2295- After a long and heavy campaign NCR territory is now under Brotherhood control. The New Desert Rangers, founded by the Courier after the Battle of Three armies are brought into the Brotherhood as a special forces branch. All NCR Rangers are stripped of their trench coats by Desert Rangers for being lackluster copies thus disbanding the NCR Rangers. It was later discovered that the NCR had systematically fragged all the former Desert Rangers who had joined them at Mojave Outpost. The Brotherhood is reunited with Lost Hills.
2296- New Vegas is absorbed into the Brotherhood Alliance as reparations for the Courier's actions. The Courier still manages to keep her position as Head of New Vegas. The Alliance starts rebuilding and re-engineering Pre-war tech. The Sierra Madre is found with the Courier's help and the Hologram tech is salvaged.
The Brotherhood Alliance sanctions a project to help solve issue of Meta-human sterility. NCR holdouts are killed at the Battle of the Boneyard by the Outcast Mercenary group.
2310- The Brotherhood Alliance sends out teams to determine the fates of other Nations of pre-war Earth. It is discovered that the Russians set up many bunkers in Siberia (The Frozen Wasteland) and the Communicator, a Russian vault dweller, managed to create a pre-war government called the Confederacy of Sovereign Republics aka the CSR. The CSR managed to organize the survivors of Europe, Britain and parts of the Middle East by Annexing them. Contact with both Nations is achieved. In the advancement of Humanity, the nations agree to rule under one banner, and the CSN are absorbed into the Brotherhood Alliance using the Phoenix of the CSN and the Gears of the Brotherhood as its sigil. Aid has been sent to fallout irradiated regions. Pre-war technology is surpassed and a space program is considered.
2319- Meta-Human sterility is solved. FEV exposure does not alter gender to asexual state during transformation instead keeping one's original gender and sexual characteristics. Many Meta-Humans undergo genetic alterations to increase their population. Breakthroughs in the project lead to genetic advances in Standard-humans as well, from increased strength and reaction times and doubling lifespans to increasing radiation resistance, but too much exposure still may lead to ghoulifacation.
An Enclave bunker is found with data on project which aimed to create the perfect humans, dubbed Omega-Humans. The project was considered a failure after the primary subjects died at Navarro during the NCR's attack.
More Synths are discovered to have been created in secret by escaped Androids and Institute remnants in Rivet City. Harkness, their leader approaches the Brotherhood peacefully. They are rebuffed and forced to go on the run.
2320- The Brotherhood Alliance begins aiding survivors of the irradiated lands and the people of many former pre-war nations are brought into the fold.
2340- Space program is started with the help of the Shi. Terraforming Mars using GECK technology being the primary goal.
2347- Prothean ruins are discovered during Terraforming operations. Seeing some Mass Effect technology as useful is incorporated into some Brotherhood technology, but the Alliance still relies heavily on its own tech seeing it as superior with the exception of Mass Effect fields. Upon seeing that the Protheans were imperialistic, the Alliance began constructing a navy of military spaceships should they return. Advances in FTL travel lead to the discovery of the Charon Mass Relay. In fear of the Protheans returning, the Brotherhood introduces new laws that require all civilians to undergo military training from a very young age. Although these laws are merely a formality as children are already trained from young ages under Brotherhood Doctrine.
Androids (Synth being considered a derogatory reference,) are allowed to join the Brotherhood by Elder Maxson himself who had a mysterious change of heart. Some conspiracy theorists believe he was replaced by an Android. The truth however is much more complicated.
2350 -The Courier announces that she stepping down as head of New Vegas in order to spend more time with her lover, Elder Veronica leaving Benny's granddaughter as her heir.
2381- The Courier dies of a heart condition that wasn't caught in time. Elder Veronica steps down a month later and dies in her sleep a day later. High Elder Maxson steps down as well to retire to Mars.
2440 - Humanity has colonized several worlds using the Mass Relays. Arcturus Station is built as a new seat of government. It is nicknamed, The New Citadel.
2561- During the activation of relay 314 near Shanxi is attacked by unknown aliens. The First Contact War begins.
A/N: Hopefully there weren't too many mistakes. Spoiler Alert: Vigil dying in the Glowing sea after taking his cure makes sense as a Deathclaw does spawn near his cave in game. Friendly hint: Don't go on that mission without power armor. Anyway, I owe that deathclaw thanks for giving me a credible reason to keep the Super Mutant cure from ever seeing the light of day.