What is the main theme of Ender's Shadow?

The main conflict in tge begining of Enders game is his relationship with the other kids in battle school. He ends up gaining the respect and [SPOILER] kills the one who is terrorizing him. The real main problem of Ender beating the formics is resolved in the end when Ender uses Dr. Device ( The Little Doctor, the MD device, or it can even be called by Mechanical Disruption Device) to blow up the formic home world and destroy the whole species