Nuclear-Weapon-Ban treaty

A nuclear weapon-ban treaty is a special agreement between countries to not use nuclear weapons. Nuclear weapons are very powerful bombs that can cause a lot of destruction. They are so powerful that if the bad guys got them, it would be very bad for everyone. So countries all around the world decide to make a special promise not to build or use nuclear weapons. It's like a promise to be good, to not use something very bad and destructive.