The Garden Wasteland, the remains of what once was the state of New Jersey. Nestled between Ghoul York and the ruins of Philadelphia, the Garden is one of the few places that still has fertile soil with the potential of being a bread basket for the mid-Atlantic region.
The Enclave, after being driven out of the Capital Wasteland, fled to Philadelphia and the Brotherhood eventually drove them into the ruins of Camden where they still are today. Camden is still riddled with raider gangs, but the Enclave is working hard to subdue them as well as to get the USS New Jersey fully operational. 
To the east is Great Lanta, the nation of freed slaves, who are in constant conflict with slaver bands in the Pine Barrens. The Pine Barrens are also home to the Pineys inbred degenerates not too dissimilar to the Swamp Folk of Point Lookout. 
Up in the Ramapo Mountains are the remains of the Ramapough nation, known today as the Keepers of the Mountains. These solitary hillfolk are wary of outsiders but some communities are open for trade. The Keepers do partake in the practice of raiding but there is one community that makes it their lifestyle; they are known as the Jackites.
Then there is Ghoul York, built out of the ruins of New York City this east coast Necropolis is composed almost entirely of ghouls and mutants. Ghoul York’s governed by various mafia style groups in an uneasy alliance, if they unite they could be a regional power.
In Paterson there are the Equalizers, a cult centered around Samuel Colt and his inventions. "God made man Samuel Colt made him equal" is their guiding philosophy, making their livelihoods manufacturing and selling weapons to those they deem worthy to receive them. Impeccable weapon smiths, they can always be found carrying their Equalizers (colt navy's) which they use to great effect against local raiders.The only people they deem unworthy are raiders and those that are already heavily armed. The latter because they don't really need the Equalizers help and they are not in true mass production yet. They also have something against energy weapons.
In Edison there are the Wizards Men, a cult worshiping Thomas Edison. Known for homemade energy weapons and a dedication to rebuilding the power grid. They are waiting for the day that the radiation levels are low enough in Ghoul York to turn the lights back on in the city that never sleeps.
Just north of Great Lanta is Long Haven. Once known as Long Beach Island, this strip of beach front paradise is now a home for all the raiders and slaves that were driven out of Great Lanta. Refurbishing old fishing and pleasure craft, they now set off on pirate raids along the Jersey coast. They are opposed on land by the Grey Guard, which are basically discount minutemen/desert rangers. The Grey Guard are also involved in conflict with the Keepers to the north.
Besides the Pineys and Grey Guard, there is another faction in the Pine Barrens. They are the Barony of the Pines, led by The Baron of the Pines they are a glorified band of raiders and slavers. Terrorizing the inhabitants of the Pine Barrens, the only thing that is feared more than them is the Jersey Devil himself.

I'm treating it as cannon in the same way Bethesda treats Tactics as cannon. The big things happened and I can pick and choose from the smaller ones. For The Garden, the Enclave after fleeing Navarro went west along I80 through Chicago to DC following Eden's call. The difference is that on their journey the Enclave picked up a cargo cult of tribals that followed them east. Once in DC President Eden ordered them purged but Col Autumn decided to send them on a suicided mission to Philly to establish a foothold in America's first capital. The Brotherhood still arrives in DC but with different reasons as to why. Originally they were sent out to reign in the Midwest brotherhood but they got lost and hit Pittsburg and they did what they did in cannon. Once the scourge is completed they come across an Enclave eyebot and Lyons decides to go to DC. To Lyons, the Enclave is his white whale that he wants to destroy most and to facilitate this he allows open recruitment of wastelanders into the Brotherhood. Project Purity is just part of a hearts and minds campaign the Brotherhood is engaged in. They Outcasts still split off and do their thing. Fallout 3 happens mostly the same as it did in canon but without the lore breaks and that the Brotherhood doesn't care about Project Purity until the Enclave gets involved. The Lone Wander passes the speech check at the end to get Autumn to leave Project Purity and he makes plans for an emergency evacuation to Philadelphia. Those loyal to Col Autumn head north while those loyal to Eden make their final stand at Raven Rock and Adams AFB. The Enclave is no longer in DC and the Brotherhood commences clean-up operations to eradicate Super Mutants in the region.

Alright now onto the stuff that happens right before The Garden. After Lyons' death, elder Maxson orders a detachment of paladins to go to Philadelphia to clear the road for the expedition to Boston. They encountered the Enclave and a force was assembled to drive them out. The Enclave was forced across the Delaware after heavy fighting. Maxson, with his obsession with destroying the Institute, denies requests to cross the Delaware to pursue the Enclave in order to launch his expedition to Boston on schedule. Leaving the Enclave to regroup and rebuild in the gang-riddled streets of Camden.