Enclave

Overview

The Enclave is a military organization that directly descended from the pre-war United States government following the Great War. Because of this, the Enclave has claimed complete authority over the country. The Enclave firmly believes that anyone not in the organization is mutated in some way and must be eradicated. This belief stems from the fact that the Enclave took shelter on an offshore drilling platform where they were safe from the nuclear war. According to them, America will never reach it's true and pure state again if mutated humans exist. 
 
Even before the Great War broke out, the United States government was still rather ruthless. The government knew that the citizens would not survive a nuclear war and believed that they would be able to successfully regroup and rebuild as long as the important people survived. The Resource War, in which major nations across the globe began scrambling to take the dwindling supply of fossil fuels for themselves, lead the United States to discover the last supply of crude oil out in the Pacific Ocean. The U.S. contracted Poseidon Oil to construct an oil rig over the supply and extract it, but before long it ran dry. However, the U.S. was not willing to give up the oil rig, and when nuclear war was just about to break out the President of the United States and several other officials fled to the drilling platform to survive. It was here that the President established a base of operations for the U.S. where they would be able to continue fighting against China. 
 

Vaults

The Vault Experiment Program is proof of how sinister the U.S. government came to be. The Vaults were advertised as being lovely places for privileged citizens to reside and survive during the nuclear war. In actuality, however, many of the Vaults were built with intentional flaws that were meant to test how Americans respond in certain situations of distress or other conditions. For example, Vault 13 included a large diversity of people and races and was designed to see how well people behaved when packed together with those of different backgrounds. Some Vaults, such as Vault 8, were operated as they were advertised but only to serve as a reference point for the others. 
 
Despite the fact that the Enclave was situated on an oil rig in the Pacific Ocean, they were able to monitor the progress of the Vaults using a large supply of high-tech equipment.  
 

The Discovery of a Lifetime

After a long time of hiding on the oil rig, the Enclave eventually decided it was probably safe to return to the mainland and start rebuilding. They sent scouting parties in Vertibirds to California just to make sure it was all clear. When the scouts arrived, they found ghouls, super mutants, and all out destruction everywhere. The leaders of the Enclave decided that anything and everything with any form of mutation would have to be eliminated. Despite the dangers, the scouting parties continued exploring and ended up discovering Mariposa Military Base. It was here that research was conducted on the Forced Evolutionary Virus preceding the Great War. The Enclave gathered up slave workers from the town of Redding and used them to dig up the abandoned base. The vats containing the F.E.V. inside were still intact, and the Enclave gathered up some samples to be sent back to the oil rig. However, the samples almost didn't make it there as the slave workers ended up mutating into super mutants and nearly killed all of the Enclave soldiers. Fortunately for them, a few troops did make it back with samples for analysis. 
 

The F.E.V. Super Toxin

Scientists from the United States Chemical Corps began work on the samples they received to develop a sort of toxin that could be used against mutations. However, the scientists needed subjects for their test in order for research to continue. They requested two groups of humans: one group containing pure, unmutated humans and the other containing mutated humans. The "unclean" test group was obtained by invading and capturing everyone from the town of Arroyo. For the "clean" population, the Enclave gathered up the inhabitants of Vault 13. Using these two groups, the scientists were successful in creating a sort of super toxin that proved to be 100% lethal against mutated subjects. The Enclave had found the ultimate anti-mutation weapon. 
 
The Enclave planned to release the toxin into the jet stream which would have resulted in the death of pretty much everything on the mainland. Unfortunately for them, the Chosen One (the protagonist from Fallout 2) arrived on the oil rig and managed to blow it up. In the process, he rescued all living test subjects. 
 

Rebirth on the East Coast

Despite the devastating losses the Enclave faced when the oil rig was destroyed, there was still a contingency of surviving forces on the mainland. These troops moved their base of operations to Raven Rock on the East Coast and were led by President John Henry Eden. Only the high-ranking scientist in charge of the group, one Dr. Autumn, and his son, Colonel Autumn, knew that Eden was actually a super artificial intelligence capable of self-awareness and direction. It was designed before the war to allow the government to continue should a horrific disaster occur. The Enclave remained shut in Raven Rock for about thirty years and really did nothing except send out Eyebots and Enclave Radio. 
 
In the year 2277 (the year that Fallout 3 takes place in), Project Purity was completed. It was essentially a large water purified that would be used to give clean water to lots of people. Eden's plan was to use the purifier to infect the Potomac River with the F.E.V. virus, similar to the previous President's plan of using the jet stream. This would, of course, result in the death of every mutated thing in the Capital Wasteland. When the Vault 101 Dweller (the main protagonist in Fallout 3) confronts Eden, he or she may agree to go with Eden's plan and plant the F.E.V. in the purifier. Alternatively, the Vault 101 Dweller can also convince the President to blow up Raven Rock himself.