The Drowned Cities by Paolo Bacigalupi
In a post-apocalyptic, no-longer-United States, Mahlia and her friend Mouse survive on the fringes of the Drowned Cities war zone. When they find and help the injured Tool, a bio-engineered part-man, part dog (plus assorted other bits), they draw the attention of the band of United Patriotic Front soldiers who are chasing him, bringing disaster down on their small community. Mouse is drafted into the UPF and must go along with their casual violence and killing or die. Tool was once part of a pack of engineered dog-man-soldiers; Mouse becomes a member of a type of human pack. The UPF, Army of God, Freedom Militia and other groups all take and retake territory, claiming to be fighting for peace. Mahlia is determined to rescue Mouse, as he once rescued her. So she and Tool set out for the Drowned Cities, where the upper floors of old skyscrapers are mined for scrap that will be sold to buy more guns. And around we go again. Should she try to save him, or should she and Tool head for the border and try to escape the war zone?