Okay kiddo, a long long time ago, there were four countries - England, Wales, Scotland and Ireland. They all had their own kings and queens and did their own thing, but sometimes they fought each other.
In the year 1603, a guy named James VI became king of Scotland and also took over as king of England and the two countries kind of became friends. Then in 1707, England and Scotland officially joined together to become one big country called Great Britain.
But Ireland was still doing their own thing. In the 1800s, England decided they wanted Ireland to be part of their big country too, so they made Ireland become part of the United Kingdom.
All the countries in the United Kingdom still have their own cultures and traditions, but they work together to make important decisions and be one big happy family!