The Sundered Lands are a dark fantasy setting, where humanity fights for survival against endless tides of undead.
In Ashe wastes resides Vorathul Nox-Kael, trying to bring ruin to the remaining civilization by sending armies of undead at the Grand Bastion - trying to break through and bring the end of humanity.
The natural barriers around the Grassland Expanse and Ironridge Hills make the Grand Bastion the only viable way through - it just needs to be breached.