1. Ideas
1.1. Training for aliens, even young kids
1.1.1. Getting all the geniuses to Fight, not for education or whatnot
1.1.1.1. The people who we thing are smart are used as soldiers, who we value as not that smart of people
1.2. Friendship
1.2.1. Friendship rising up from compassion
1.2.1.1. They all are in same situation, away from their parents/home, getting trained for war
1.2.1.1.1. So even who were once-enemies, like Ender and the other gang become really good friends
2. Characters
2.1. Ender
2.1.1. Autistic
2.1.1.1. The way he thinks is completely different from normal kids
2.1.1.1.1. For example, when he beats up that little kid in the beginning of the book, he finds the most efficient and effective way to beat that kid up
2.1.2. Genius
2.1.2.1. Figuring out how 4 dimensional traveling works
2.2. The observers
2.2.1. Don't know whether they're cruel or smart in training these little kids