as far as I can tell the campaigns are interconnected, meaning that they all happen at the same time only from different view points...
so to get the whole story I think you need to play all the campaigns /and if you want it chronologically play all the first scenarios from each faction, after that all the second ones etc./
spoiler for the storySpoiler:
did a little searching and found this [Edited by YamiSoran, 10/20/2011 5:30:12 AM]
A legendary Archangel general, revived hundreds of years after perishing during the Elder Wars, plots to recover his powers and take control of Ashan while battling a supposed Demon invasion, but is impeded by the Griffin dynasty, led by Duke Slava. As a war erupts between them, Slava is assassinated in his throne, leaving behind as heirs his five children — Anton (Haven), Anastasya (Necropolis), Kiril (Inferno), Sandor (Stronghold) and Irina (Sanctuary).