The Vogon Constructor Fleet (according to 'TheHitchhikersGuideToTheGalaxy') was sent to Earth to destroy it. You see, Earth was right in the path of a new intergalactic super highway. Obviously, the human race was quite upset about this event, but hey, the plans were on hand at the galactic planning office for all to see for several years. Tough luck Earth, and good luck Arthur Dent!