Ender's Game by Orson Scott Card

A young prodigy is enlisted into a military academy in space, where he is trained through complex war games to combat an impending alien invasion. Despite his initial struggles with isolation and manipulation by the academy's leaders, he rises through the ranks due to his strategic genius and leadership skills. The protagonist grapples with the moral implications of war and the cost of his own humanity, as he is groomed to be the Earth's ultimate weapon against the alien threat.

The 1062nd greatest book of all time