Power transition theory is like a game of kids playing with toys. If one kid has a better or bigger toy than the others, they are more likely to be in charge of the game. And if another kid gets a better or bigger toy, they might become the new boss.
In the world of grown-ups, countries are like the kids and their toys are things like military power, economic resources, and political influence. In power transition theory, scholars try to predict what will happen when one country gets a lot of power, and whether they will be able to keep it or if another country will try to take it away.
Sometimes, when there's a big change in the balance of power between countries, it can lead to war. This is like when one kid says “I'm the boss of this game now!” and another kid says “No way, I want to be in charge”.
So, power transition theory is all about studying how countries gain and lose power over time, and how these changes can affect relationships between countries. Just like kids, countries can either play nicely with each other and share the toys, or they can fight over them.