An African tribe called the Ik throws their children out of their homes once they turn 3. They are left to fend for themselves with no help from their parents at all, and to survive, form groups with others their age. These groups only last a few years, and every so often the individual will join a completely different group.
An army and navy who work in the same way as others except their rank titles are upside-down. So people start as full generals and those with the rank of private command armies.