David Mitrany was a very smart man who lived a long time ago and studied how countries work together. He noticed that sometimes countries don't work well together because they have different ways of doing things or different ideas. It's kind of like if you and your friend wanted to play a game but you couldn't agree on what game to play.
So, David Mitrany came up with an idea that countries could work together on small things that they all agreed on, even if they had different ideas about bigger things. It's kind of like if you and your friend couldn't agree on a game to play, but you both liked drawing, so you decided to draw together instead.
David Mitrany believed that if countries worked on small things together, like trading and sharing ideas, then they would become closer and more likely to work together on bigger things like making peace.
He thought that countries should belong to groups called "functional organizations" that focus on one thing, like trading or transportation. And if these functional organizations worked together, then countries would become more connected and peaceful.
Overall, David Mitrany was a smart man who believed that countries could work together by focusing on small things that they all agreed on, and by belonging to groups that focus on one thing at a time.