Okay, kiddo, so the Copenhagen School is a fancy group of people who study how countries talk to each other and make decisions together (kind of like how you talk to your friends and make decisions about what game to play).
They believe that the way countries talk to each other is really important, and they pay special attention to things like language and culture.
They also think that the things we say and how we say them can actually affect how we think and act, which is pretty cool!
For example, let's say your friend wants to play tag, but you don't want to. If you say "no thanks" in a really mean tone of voice, your friend might feel bad and think you don't like them. But if you say "no thanks" in a friendly tone of voice and suggest a different game, your friend will probably feel happy and excited to play something else.
So the Copenhagen School basically looks at how leaders of different countries use language and how that affects the way they treat each other. They also think about how these interactions can lead to bigger conflicts or even wars.
But don't worry, kiddo, these people are working really hard to make sure countries can talk to each other nicely and avoid fighting.