The world has broken down. In attempt to rebuild civilation a world government is formed, ruled by a cruel face-less man. To keep the world in order, he steals an idea from one of the most popular piece of teenage literature of the age.
He steals all surviving children, from 12 to 18 years, and splits them into districts. To keep the families in order, and to punish them for the previous destruction they caused the Earth, he forces the children to play the Games.
The Hunger Games.