Psychological warfare is when people use different kinds of techniques to influence or try to change the opinions and beliefs of others. It is a way of using psychology to influence or scare people away from doing something. For example, a country might use psychological warfare to try to convince a group of people to not join an army or a movement. They might do this by spreading false information, making people afraid of a certain kind of punishment, or by trying to make people think that what they want isn't worth it.