Earth was a mess. The downfall actually began in the early part of the century with the colonization of Mars and Venus. All the good jobs were off-planet. People deserted Earth like rats fleeing a sinking ship. And - as usual with humans - within a generation or so, those unlucky enough not to have been born on Mars or Venus were looked down on. Branded as second-class citizens, they were usually regulated to the slums of the new worlds or simply not allowed off Earth itself.