Buffy/Angel Canon Timeline
2002 – Los Angeles – Angel Investigations unwittingly brings the Supernatural into the limelight during a near apocalypse. For several weeks, the sun is blotted out over LA followed by the arrival of a “divine” being known as Jasmine. After these events, most of it was swept under the rug (so to speak) and people eventually chalked it up to exaggeration or urban myth…or outright hoax. A few , however, knew the truth. Namely the people that lived in LA at the time and were under the spell of Jasmine.
2003 – Sunnydale – The First Evil is destroyed when Buffy Summers concocts a daring plan: Using Willow Rosenburgs astounding magical talents, alter the actual magic used to create the Slayer line. Instead of one Slayer, any potential slayer would now be a Slayer. The recently ensouled Vampire named Spike sacrificed himself to save the Slayer and her friends. In the process Sunnydale is completely destroyed. The Slayer and company take a well deserved year or two off to lick their wounds and train the new Slayers flowing their way from all over the world.
2003 – Meanwhile in Los Angeles, an Old One is resurrected into the body of a mortal woman. Named Illyria, she is effectively “leashed” by Angel Investigations (now working from within the belly of the beast at Wolfram and Hart). Angel concocts his own daring plan much as Buffy did… take the fight directly to the Senior Partners by eradicating their entire secret society responsible for most of the prime evils of the world: The Circle of the Black Thorn.
2003 – After the above events with Angel, the Senior Partners send LA (yes, all of it) into Hell. Angel and company face many trials there. The outside world thinks LA is perfectly fine, thanks to a supremely powerful Glamour.
There is more, but I am unsure I want to use it in the campaign, or what year this should all take place in . I kinda like just “handwaving” and letting the story start now (2013) and I can fill shit in as I wish.