The main idea behind all the campaigns revolves around one particular yet to be Named evil being. This idea centers around a very old Horror who, for reasons unknown, split itself into 13 different artifacts. Each item signifies and amplifies a different form of energy that the Horror originally drew nourishment from, ranging from Pain, to Fear, to Pride, to Deceit.
The first group has already encountered a few of the artifacts, unknowingly. As for the other two groups, they have yet to have a straight encounter with the 13, but they will soon. This idea is from a starting adventure that one of my players had, but he lost all the info in it, so stopped.
I picked up where he left off and adapted it to cover all three groups. This way I could have a major campaign with several players and not run into the need for making new arch villians.
With each group battling a few of the 13, but never really meeting each other, this ensures that the Horror itself will never reform, but never be truly destroyed. Although the whole thing sounds complex, and it is, the game is really fun and keeps all the players up and running.
For additional info on the 13, go here --->