Ender's War by Orson Scott Card

This science fiction novel follows a young prodigy named Ender Wiggin, who is recruited into an advanced military academy in space to prepare for an impending alien invasion. In a future where Earth has barely survived two conflicts with the Formics, an insectoid alien species, Ender is trained through increasingly difficult war games in zero gravity to develop tactics and leadership skills. As he progresses, Ender struggles with the isolation, manipulation by the military leaders, and the moral implications of his actions in simulations that become disturbingly realistic. The novel explores themes of leadership, the ethics of war, and what it means to truly understand one's enemy. The 12174th greatest book of all time