Hellforge posted an editorial about how the Fallout 3 main plot recycles much of the plots of all previous published Fallout games: Fallout, Fallout 2, Fallout Tactics and Fallout: Brotherhood of Steel:

The Brotherhood Of Steel
In both Fallout Tactics and Fallout 3, the player is forced to join a splinter faction within the Brotherhood of Steel in order to continue the storyline. In the first Fallout, joining the Brotherhood was simply optional. They barely played a role in Fallout 2, and in the unreleased Van Buren, they declined in power due to an on-going war with the New California Republic. It should be noted that Fallout 3 takes place many years after the events of Fallout 2, so their presence in Washington D.C. is confusing.
Similarities to FOBOS
Fallout: Brotherhood of Steel, or FOBOS as it is known is an immensely unpopular action game that took apart the Fallout setting for the purpose of making Interplay a quick buck by being released as a generic console title.
That being said, the game shares similarities with Fallout 3's plot, in that both games feature a Vault full of FEV, which by all accounts in the original RPGs are a rare, classified substance, and both games feature a Brotherhood of Steel elder forming a splinter faction in a location remote from the organization's headquarters, against council orders, in order to deal with a Super Mutant threat.
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