This article is about the processes. For a list of destroyed planets, see Category: Destroyed Planets.
First of all, the fact that you're reading this may indicate that you're a psychopath who wants to destroy a planet. If so, please turn yourself in to the Space Police immediately.
There are many processes whereby a planet may naturally be "destroyed". Depletion of resources by its native species is a common cause, though some claim this doesn't count because the planet is technically still there. Planets can be obliterated by asteroid strikes, their suns going supernova and/or becoming black holes, or by a guy named Galactus who likes to eat them.
The prospect of destroying a planet was once technologically and morally unthinkable to most beings, aside from Galactus. However, technological and amoral developments have made it childs' play in many circles. Massive space stations known as the Death Star and Death Star II were among the first superweapons developed for this purpose, though it was claimed but never demonstrated that the earlier and somewhat smaller satellite Trigon One could do it as well.
Elsewhere and much later, similar technology evolved to the point where it could be spread out collectively amongst the ships of a Vogon Constructor Fleet, and planets could be routinely demolished for development purposes. At one point a planet in the Seventh Dimension was reportedly used as a ball in a game of intergalactic bar billiards and potted into a black hole. Tragically, it only scored thirty points.