Why isn't Pluto a planet anymore?

Pluto is considered a dwarf planet instead of a full-sized planet like Earth, Mars, and the other six planets in our Solar System. The International Astronomical Union uses three rules to decide whether something is a planet or not. The first rule is that it must be orbiting the sun. The second rule is that it must be round or nearly round. The last rule is that it has “cleared the neighborhood” around its orbit, which means it must not have other bodies of similar size in its orbit. A way to understand this third rule is by imagining that each planet is a ball, and its orbit is a tube around the sun. The tube is a little bigger than the “ball,” or planet. If there are other “balls” or celestial objects in the orbit and the planet cannot move them out of the way because it doesn’t have enough gravitational force, then it has not “cleared the neighborhood.” Pluto follows the first two rules, but not the third, so it has been changed from a planet to a dwarf planet. Pluto is in the same orbital neighborhood as other objects in the Kuiper Belt like other dwarf planets and comets.