The Ash Wall by Brenden Bryan

Beyond the Wall, humanity survives.
Behind it, humanity rots.

Seventeen-year-old Rowan Vale has spent his entire life in the Fields, where farmers surrender their harvests—and their children—to the powerful rulers of the Heights. The people above promise protection, order, and survival.

They're lying.

After discovering a terrifying secret hidden beneath the Wall, Rowan is pulled into a deadly rebellion that stretches from starving underground cities to the glittering towers above the poisoned clouds. Hunted by ruthless soldiers, betrayed by family, and forced to trust the daughter of the enemy, Rowan must uncover the truth before the Heights erase the Fields forever.

But the deeper he goes, the worse the truth becomes.

Because the Wall was never built to protect humanity.

It was built to feed something.