In this book when different groups arrived in America (Vikings, the Irish, Eastern Russians), they brought their Gods with them, and they believed in them so deeply they were made flesh. As people developed, however, they started believing in other things. The old Gods didn't disappear, however, and they ended up living on the fringes of society in an effort to survive. This naturally upsets them, so they decide to put up one last stand against these newer Gods.
I don't like these books, because they ask you to accept things I didn't like on trust. So blah, I'm not impressed. Don't get me wrong, it was well written though.