Weapons designed for everyone are an advantage at war, but they can also be extremely devastating. Experts test the three most important weapons that can be learned quickly. The crossbow transforms peasants into warriors that suddenly become a threat to the knight; learning to use a pike is easy but requires bravery. The Kalashnikov is considered the world’s deadliest weapon due to its rare simplicity, but if 3D printed guns go into mass production, world peace will never be the same.