In his classic A Short History of the World, H.G. Wells asked why the Roman Empire grew, and why it so completely decayed.
He concluded that it grew because the idea of citizenship held it together, creating a sense of privilege and obligation and a willingness to make sacrifices in the name of Rome.
However, the failure to explain itself to its increasing multitude of citizens, or invite their co-operation, led to the demise of its collective mission.
