How are homing pigeons trained to deliver messages? Why don't they just fly away? How can someone tell them where to deliver the messages?
They are not trained. As stated in https://en.wikipedia.org/wiki/Homing_pigeon and https://en.wikipedia.org/wiki/Pigeon_post the homing pigeon was selectively bred to have the ability to figure out where its home is over particularly long distances. The pigeon just needs to be raised in a location to consider that place its home, and it will naturally want to fly back when separated from its home. As a result, each pigeon could only be used to deliver to one location, and people would have to raise pigeons according to where they might want to send messages in the future. Homing pigeons have also been known to make mistakes when flying home as well, or they have been killed along the way. Therefore, in order to insure messages were received, multiple birds with the same message might be sent.