So imagine you're in a big game of make-believe, like pretend you're a king or queen in a castle. In Ireland a long long time ago, some people played a game like that and they called it the Kingdom of Dublin.
The Kingdom of Dublin was a pretend kingdom, kind of like when you play pretend with your friends. But it was special because some real people actually lived there and pretended to be kings and queens too!
The Kingdom of Dublin was located in Ireland, and it was ruled by a group of Vikings, who were really good at sailing ships and had traveled all the way from Norway to get there. They liked Dublin because it had a big river, called the Liffey, which made it easy for them to trade goods with other countries.
Even though the Vikings were in charge in the Kingdom of Dublin, other people also lived there. There were Irish people, who had been there for a long time, and other Vikings who had come from other places.
So the Kingdom of Dublin was a pretend kingdom ruled by Vikings, but it was also a real place where lots of different people lived. People had to work together to make it a good place to live, just like when you and your friends play pretend together and make up rules to keep everyone happy.