Pelo comentário do OP acima, isso provavelmente foi Fora da boca do dragão (2003) por Mark Geston.
Um sumário do lote de goodreads.com mostra alguns detalhes correspondentes:
Amon VanRoark heard the prophet speaking in the marketplace of the decaying city. Timonias spoke with all the glowing words and crystal clarity of his calling. And the young man listened and he followed. The call was to the Meadows, to the Wars, to the Armageddon in which all the forces of Good and all the forces of Evil would meet, would clash, would decide the fate of the already doomed world. There had been other Armageddons, false ones, so Amon believed, in the lifetimes of his father, and his grandfather before him. But when Amon looked at the ruined world around him, at the lost technologies, the vestiges of dying cultures, the warped rays of the sun, he knew he must answer the call to this last Armageddon, in which Creation would either be renewed or finally be let to end.