Thaidakar the Ghostblood

so, this guy wakes up in the middle of a field. He has no memories; unless a desire could be called a memory. Or, purpose would be more accurate. All he knows is that he needs to destroy the world. Not why, not how, just that he needs to do it. He and another character (who's gonna be another protagonist) meet and become fast friends, they try to get to the capital of the land to see if anyone there can help him. As they start their journey, they stumble upon the giant camp of a large army. Or armies. whichever description works for you. Suffice it to say, the army is the guy's army. He is thrust upon the leadership of an army wanting to destroy a peace loving kingdom. But why?