Orson Scott Card: Shadow of the Giant (Ender, Book8)

Description

He knew he could not survive through strength; he used his tactical genius to gain acceptance into a children's gang, and then to help make that gang a template for success for all the others. He civilized them, and lived to grow older. Then he was discovered by the recruiters for the Battle School. For Earth was at war -- a terrible war with an inscrutable alien enemy. A war that humanity was near to losing. But the long distances of interstellar space has given hope to the defenders of Earth -- they had time to train military geniuses up from childhood, forging them into an irresistible force in the high-orbital facility called the Battle School. That story is told in two books, the beloved classic Ender's Game, and its parallel, Ender's Shadow.