I'd have to say weapons. Every weapon ever made. I'm sure originally, weapons were made for hunting animals. But somewhere along the line, the men of old started fighting themselves and the weapons we made for hunting animals were used for hunting ourselves. Over the years we've just kept on improving and improving so we can kill ourselves more effectively. From arrows to swords to cannons to guns to bombs. We are just getting worse and truthfully, he world would be a better place without weapons