The Clockwork Century by Cherie Priest is steampunk book series set in an alternate history.
Series Synopsis
It is 1880. The American Civil War has raged for nearly two decades, driving technology in strange and terrible directions. Combat dirigibles skulk across the sky and armored vehicles crawl along the land. Military scientists twist the laws of man and nature, and barter their souls for weapons powered by light, fire, and steam.
But life struggles forward for soldiers and ordinary citizens. The fractured nation is dotted with stricken towns and epic scenes of devastation—some manmade, and some more mysterious. In the western territories cities are swallowed by gas and walled away to rot while the frontiers are strip-mined for resources. On the borders between North and South, spies scour and scheme, and smugglers build economies more stable than their governments.
This is the Clockwork Century. It is dark here, and different.