This excellent book, which was later immortalized as a pretty bad Costner movie, contains three observations which I think are relevant here.
Set in post-collapse America, Postman follows the life of a regular guy and his adventures trying to survive in the new hostile world.
Point 1 - From the main character's point of view, (and pretty much everyone else), he doesn't really know what brought on the collapse. Things get dicey, and before he knows it, the life he knew has disappeared. In fact, we discover that the initial cause of the crisis becomes unimportant when compared to how America, and indeed the world, reacts to the crisis. Brin is suggesting that no matter how bad the events which lead to the crisis are, it is our lack of unity which dooms mankind. Unable to band together and work toward a solution, man sinks back into the violent and terrible times of his past.
Point 2 - The bad guys in the book are the Holnists. A brutal militia which pillages the remaining population, they provide a common enemy for the small villages & hamlets in the battle for survival. Some communities are able to resist by force, but most simply pay the required tribute. This common threat binds the small communities in the effort to resist their influence.
Point 3 - Quite by accident, Gordon finds a new way to support himself. He finds a postal jeep in the forest, and to survive, puts on the carriers old uniform. He finds that a simple but bold lie. of a restored US, combined with a bag of pre-collapse mail, are a virtual passport into the remaining communities. What begins as a survival strategy, grows as Gordon travels from town to town as "the postman". I won't spoil the ending... but it becomes clear, that it is the simple concept of service which restores hope for the hopeless. This idea of unselfish service unites the dispersed communities like nothing else could. Old timers weep, remembering the good ole days, while youngsters are amazed at this man, who isn't acting for simple personnel survival, like everyone they have ever met, but rather acts to benefit people he does not even know.
Our current culture behaves like a teenager who's parents are out of town. Invite over everyone you know, munch all the food, drink all the booze, trash the place. Who cares? The fridge automatically gets stocked again, and the booze refills as if by magic. (perhaps it's abiotic) And the maid cleans up the mess...
Maybe we deserve to be grounded...
And maybe, as in the postman, we need a common enemy, and a simple idea, to finally unite as a world, and emerge in our collective future, as adults.





