THE GREAT IRON WAR by Dean F. Wilson
In the world of Altadas, there are no more human births. The Regime is replacing the unborn with demons, while the Resistance is trying to destroy a drug called Hope that the demons need to survive.
Between these two warring factions lies Jacob, a man who profits from smuggling contraceptive amulets into the city of Blackout. He cares little about the Great Iron War, but a chance capture, and an even more accidental rescue, embroils him in a plot to starve the Regime from power.
When Hope is an enemy, Jacob finds it harder than he thought to remain indifferent. When the Resistance opts to field its experimental landship, the Hopebreaker, they find they might just have a chance to win this war.