City of Refuge (The Fifth Sacred Thing Book 3);

Every city needs three things: a plaza, a hearth, and a sacred tree...
In the violent, desperate world of 2048, eco-catastrophes and societal breakdown have left the country splintered. Yet amidst the ruins stands a green and flourishing city where four things are sacred—Air, Fire, Water, and Earth. When the ruthless Stewards of the Southlands invade, the people of Califia defeat them using nonviolence and magic. But they’ll be back, unless the northerners can liberate the Southlands first.
Healer Madrone struggles to repair the wounds of war and deprivation. Soldier/defector River leads an Army of Liberation to the south. Bird, musician turned guerrilla, longs to return to the fight, but now he’s pledged to deeper powers. How can they build a new world when people are so deeply wounded by the old?
Madrone has a dream... Build a city of refuge in the heartland of the enemy.