The Greatwinter Trilogy

Two millennia from now, there is no more electricity, wind engines are leading-edge technology, librarians fight duels to settle disputes, steam power is banned by every major religion, and a mysterious siren "Call" lures people to their watery graves. Nevertheless. a brilliant and ruthless leader intends to start an improbable war: a war against inconceivably ancient nuclear battlestations orbiting Earth. However, the greatest threat to humanity is not these ancient weapons, but a demented and implacable enemy who has resurrected an obscene and evil concept from the distant past...

Comprising the novels Souls in the Great Machine, The Miocene Arrow, and Eyes of the Calculor.