The Scorpion Rules by Erin Bow
Four centuries after an artificial intelligence named Talis conquered the world, the United Nations keeps the peace by holding the world leaders' children hostage. If war breaks out, the children die. Talis's hostage, Crown Princess Greta, is resigned to the death that will claim her if she fails to reach her 18th birthday. But a hostage boy from a new American alliance stirs rebellion in Greta when he takes a stand. Read a sample.